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        <title>Frontiers in Electronic Materials | Superconducting Materials section | New and Recent Articles</title>
        <link>https://www.frontiersin.org/journals/electronic-materials/sections/superconducting-materials</link>
        <description>RSS Feed for Superconducting Materials section in the Frontiers in Electronic Materials journal | New and Recent Articles</description>
        <language>en-us</language>
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        <pubDate>2026-05-13T14:08:32.359+00:00</pubDate>
        <ttl>60</ttl>
        <item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2025.1572940</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2025.1572940</link>
        <title><![CDATA[Characterizing sample degradation from synchrotron based X-ray measurements of ultra-thin exfoliated flakes]]></title>
        <pubdate>2025-06-25T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>M. F. DiScala</author><author>V. Hsieh</author><author>B. S. Jessen</author><author>Y. Gu</author><author>D. J. Rizzo</author><author>J. M. Amontree</author><author>X. Yan</author><author>Q. Wang</author><author>M. Kapfer</author><author>T. Kim</author><author>M. Geiwitz</author><author>G. Natale</author><author>J. Pelliciari</author><author>J. C. Hone</author><author>K. S. Burch</author><author>D. N. Basov</author><author>C. R. Dean</author><author>V. Bisogni</author><author>K. W. Plumb</author>
        <description><![CDATA[It is undeniable that novel 2D devices and heterostructures will have a lasting impact on the advancement of future technologies. However, the inherent instability of many exfoliated van der Waals (vdW) materials is a well-known hurdle yet to be overcome. Thus, the sustained interest in exfoliated vdW materials underscores the importance of understanding the mechanisms of sample degradation to establish proactive protective measures. Here, the impact of prolonged synchrotron-based X-ray beam exposure on exfoliated flakes of two contemporary vdW materials, NiPS3 and α-RuCl3, is explored using resonant inelastic X-ray scattering (RIXS) and total fluorescence yield X-ray absorption spectroscopy (XAS). In NiPS3, the resulting RIXS and XAS spectra show a suppression, then vanishing, of NiS6 multiplet excitations coupled with an upward shift of the peak energy of the XAS as a function of X-ray dose. In α-RuCl3, the signs of beam damage from the RIXS spectra are less evident. However, the post-experiment characterization of both materials using Raman spectroscopy exhibits signals of an amorphous and disordered system compared to pristine flakes; in addition, energy-dispersive X-ray spectroscopy of NiPS3 shows evidence of ligand vacancies. As synchrotron radiation is fast becoming a required probe to study 2D vdW materials, these findings lay the groundwork for the development of future protective measures for synchrotron-based prolonged X-ray beam exposure, as well as for X-ray free electron laser.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2025.1456147</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2025.1456147</link>
        <title><![CDATA[Excitonic insulator candidate Ta2NiSe5 and related transition-metal compounds studied by resonant inelastic x-ray scattering]]></title>
        <pubdate>2025-02-06T00:00:00Z</pubdate>
        <category>Mini Review</category>
        <author>Takashi Mizokawa</author><author>Claude Monney</author>
        <description><![CDATA[Resonant inelastic x-ray scattering (RIXS) can probe electron-hole excitations in excitonic insulators (EIs) which are realized by Coulomb attractive interaction between electrons and holes in semimetals or narrow gap semiconductors. In the present article, we review the exotic electronic state of an EI candidate Ta2NiSe5 which is probed by Ni 2p-3d RIXS as well as Ni 2p x-ray photoemission/absorption spectroscopy. The RIXS results on the exotic electronic state under the electron-hole and electron-lattice correlations suggest requirement of a new theoretical scheme which can describe itinerant electron-hole excitations and the localized charge-transfer excitations as well as the electron-lattice interaction.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2024.1473324</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2024.1473324</link>
        <title><![CDATA[Dynamic charge order from strong correlations in the cuprates]]></title>
        <pubdate>2024-11-13T00:00:00Z</pubdate>
        <category>Review</category>
        <author>Eduardo H. da Silva Neto</author><author>Alex Frano</author><author>Fabio Boschini</author>
        <description><![CDATA[Charge order has been a central focus in the study of cuprate high-temperature superconductors due to its intriguing yet not fully understood connection to superconductivity. Recent advances in resonant inelastic x-ray scattering (RIXS) in the soft x-ray regime have enabled the first momentum-resolved studies of dynamic charge order correlations in the cuprates. This progress has opened a window for a more nuanced investigation into the mechanisms behind the formation of charge order (CO) correlations. This review provides an overview of RIXS-based measurements of dynamic CO correlations in various cuprate materials. It specifically focuses on electron-doped cuprates and Bi-based hole-doped cuprates, where the CO-related RIXS signals may reveal signatures of the effective Coulomb interactions. This aims to explore a connection between two central phenomena in the cuprates: strong Coulomb correlations and CO-forming tendencies. Finally, we discuss current open questions and potential directions for future RIXS studies as the technique continues to improve and mature, along with other probes of dynamic correlations that would provide a more comprehensive picture.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2024.1487856</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2024.1487856</link>
        <title><![CDATA[Advances in hard X-ray RIXS toward meV resolution in the study of 5d transition metal materials]]></title>
        <pubdate>2024-10-03T00:00:00Z</pubdate>
        <category>Perspective</category>
        <author>Jungho Kim</author><author>Xiangrong Huang</author><author>Thomas Toellner</author><author>Ayman Said</author>
        <description><![CDATA[Resonant inelastic X-ray scattering (RIXS) has played a pivotal role in advancing our understanding of spin-orbit physics in 5d transition metal materials. The progress in RIXS techniques has closely paralleled improvements in energy resolution, which have enabled the study of very low-lying excitations and led to the discovery of numerous new phenomena with significant scientific and technological implications. The multi-bend achromat (MBA) lattice upgrade of third-generation synchrotron sources, such as the Advanced Photon Source (APS), heralds a transformative era by introducing enhancements in brilliance and emittance. These advancements provide an opportunity to push the boundaries of RIXS techniques, meeting the challenges at the research frontiers of material science. This article aims to highlight key instrumental and technical advancements that enable the achievement of meV resolution in RIXS and discuss the impact of such high-resolution RIXS on exploring spin-orbit physics in 5d transition metal materials.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2024.1392760</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2024.1392760</link>
        <title><![CDATA[Uniaxial stress effect on the electronic structure of quantum materials]]></title>
        <pubdate>2024-05-09T00:00:00Z</pubdate>
        <category>Review</category>
        <author>Na Hyun Jo</author><author>Elena Gati</author><author>Heike Pfau</author>
        <description><![CDATA[Uniaxial stress has proven to be a powerful experimental tuning parameter for effectively controlling lattice, charge, orbital, and spin degrees of freedom in quantum materials. In addition, its ability to manipulate the symmetry of materials has garnered significant attention. Recent technical progress to combine uniaxial stress cells with quantum oscillation and angle-resolved photoemission techniques allowed to study the electronic structure as function of uniaxial stress. This review provides an overview on experimental advancements in methods and examines studies on diverse quantum materials, encompassing the semimetal WTe2, the unconventional superconductor Sr2RuO4, Fe-based superconductors, and topological materials.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2024.1403513</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2024.1403513</link>
        <title><![CDATA[Editorial: Progress on superconducting materials for SRF applications]]></title>
        <pubdate>2024-04-17T00:00:00Z</pubdate>
        <category>Editorial</category>
        <author>Pashupati Dhakal</author><author>Tsuyoshi Tajima</author><author>Marc Wenskat</author>
        <description></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2024.1401752</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2024.1401752</link>
        <title><![CDATA[Corrigendum: Characterization of dissipative regions of a N-doped superconducting radio-frequency cavity]]></title>
        <pubdate>2024-04-03T00:00:00Z</pubdate>
        <category>Correction</category>
        <author>Eric M. Lechner</author><author>Basu Dev Oli</author><author>Junki Makita</author><author>Gianluigi Ciovati</author><author>Alex Gurevich</author><author>Maria Iavarone</author>
        <description></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2024.1339293</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2024.1339293</link>
        <title><![CDATA[Magneto-thermal limitations in superconducting cavities at high radio-frequency fields]]></title>
        <pubdate>2024-03-08T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>I. Parajuli</author><author>G. Ciovati</author><author>A. Gurevich</author>
        <description><![CDATA[The performance of superconducting radio-frequency Nb cavities at high radio-frequency (rf) fields in the absence of field emission can be limited by either a sharp decrease of the quality factor Q0(Bp) above peak surface magnetic fields Bp ∼100 mT or by a quench. We have measured Q0(Bp) at 2 K of several 1.3 GHz single-cell Nb cavities with different grain sizes, and with different ambient magnetic fields and cooldown rates below the critical temperature. Temperature mapping and a novel magnetic field mapping systems were used to find the location of “hot-spots” and regions of trapped magnetic flux. The use of a variable input coupler allowed further exploring the dissipative state. The results showed a remarkable thermal stability in some cavities with up to 200 W of rf power dissipation at 2 K, whereas other cavities quenched at much lower rf power. We observed a narrow distributions of the onset fields of hot-spots which were not affected by thermal cycling or by conditions which favor the formation of Nb hydrides. Furthermore, a poor correlation was found between the location of hot-spots and trapped vortices. We suggest that the totality of our experimental data can be explained by a sharp increase of the residual surface resistance above 120–140 mT due to the field-induced breakdown of a proximity-coupled metallic suboxide layer at the surface.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2024.1346235</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2024.1346235</link>
        <title><![CDATA[SRF material research using muon spin rotation and beta-detected nuclear magnetic resonance]]></title>
        <pubdate>2024-02-15T00:00:00Z</pubdate>
        <category>Review</category>
        <author>Tobias Junginger</author><author>Robert Laxdal</author><author>W. A. MacFarlane</author><author>Andreas Suter</author>
        <description><![CDATA[Muon spins precess in transverse magnetic fields and emit a positron preferentially in the spin direction at the instant of decay, enabling muon spin rotation (μSR) as a precise probe of local magnetic fields in matter. μSR has been used to characterize superconducting radio-frequency (SRF) materials since 2010. At TRIUMF, a beam of 4.2 MeV μ+ is implanted at a material-dependent depth of approximately 150 μm. A dedicated spectrometer was developed to measure the field of first vortex penetration and pinning strength in SRF materials in parallel magnetic fields of up to 300 mT. A low-energy beam available at PSI implants μ+ at variable depth in the London layer allowing for direct measurements of the London penetration depth from which other material parameters relevant for SRF applications, such as the lower critical field and the superheating field, can be calculated. Beta-detected nuclear magnetic resonance (β-NMR) is a technique similar to low-energy μSR using beams of low-energy β radioactive ions. With a recent upgrade, it is capable of detecting the penetration of parallel magnetic vortices, depth resolved with nanometer resolution at applied fields of up to 200 mT. In this paper, we review the impact and capabilities of these techniques for SRF research.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2023.1323404</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2023.1323404</link>
        <title><![CDATA[Pair density wave and superconductivity in a kinetically frustrated doped Emery model on a square lattice]]></title>
        <pubdate>2023-11-28T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Hong-Chen Jiang</author><author>Thomas Peter Devereaux</author>
        <description><![CDATA[The quest to understand the nature of superconductivity in the cuprates has spotlighted the pair density wave (PDW)–a superconducting state characterized by a spatially modulated order parameter. Despite significant advances in understanding PDW properties, conclusively demonstrating its presence in systems pertinent to cuprate superconductors remains elusive. In this study, we present a systematic density-matrix renormalization group study to investigate the Emery model (or the three-band Hubbard model) on two-leg square cylinders with negative electron hopping term tpp between adjacent oxygen sites. Kinetic frustration - introduced by changing the sign of oxygen-oxygen hopping - leads to a much reduced Cu-Cu antiferromagnetic exchange along with an enlarged charge transfer energy that changes the local properties of the model. At light doping levels, our findings reveal a ground state remarkably consistent with a PDW, exhibiting mutually commensurate superconducting (SC), charge, and spin density wave correlations. Intriguingly, the dominant SC pairing is observed between neighboring oxygen sites, diverging from the expected Cu sites in the positive tpp case. When the system incorporates moderate near-neighbor interactions, particularly an attractive Vpp between adjacent oxygen sites, the SC correlations become quasi-long-ranged, accompanied by a pronounced divergence in the PDW susceptibility. When the attractive Vpp increases further, the system gives way to an unconventional d-wave superconductivity.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2023.1257490</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2023.1257490</link>
        <title><![CDATA[Electron-hole asymmetry in the phase diagram of carrier-tuned CsV3Sb5]]></title>
        <pubdate>2023-10-24T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Andrea N. Capa Salinas</author><author>Brenden R. Ortiz</author><author>Calvin Bales</author><author>Jonathan Frassineti</author><author>Vesna F. Mitrović</author><author>Stephen D. Wilson</author>
        <description><![CDATA[In this work, we study the effect of electron doping on the kagome superconductor CsV3Sb5. Single crystals and powders of CsV3Sb5−xTex are synthesized and characterized via magnetic susceptibility, nuclear quadrupole resonance, and x-ray diffraction measurements, where we observe a slight suppression of the charge density wave transition temperature and superconducting temperature with the introduction of electron dopants. In contrast to hole doping, both transitions survive relatively unperturbed up to the solubility limit of Te within the lattice. A comparison is presented between the electronic phase diagrams of electron- and hole-tuned CsV3Sb5.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2023.1244126</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2023.1244126</link>
        <title><![CDATA[Mid-T heat treatments on BCP’ed coaxial cavities at TRIUMF]]></title>
        <pubdate>2023-10-09T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>P. Kolb</author><author>Z. Yao</author><author>A. Blackburn</author><author>R. Gregory</author><author>D. Hedji</author><author>M. McMullin</author><author>T. Junginger</author><author>R. E. Laxdal</author>
        <description><![CDATA[Mid-T heat treatments in the range from 250°C to 400°C on superconducting radio-frequency (SRF) cavities have been shown to provide high quality factors that rise with applied rf field strength in high frequency, electro-polished (EP), elliptical cavities operating at 2 K, similar to nitrogen doped cavities. The rise in quality factor is attributed to a decrease in the temperature dependent part of the surface resistance RBCS. Until now, no results have been reported for these new treatments on quarter-wave resonators (QWR) and half-wave resonators (HWR). The TRIUMF multi-mode coaxial cavities are dedicated test cavities that allow frequency and temperature resolved performance characterization of treatments without changing environments, therefore providing an excellent test vehicle to test these new treatments with rf frequencies ranging from 200 to 1,200 MHz. In this paper, performance measurements from both QWR and HWR cavities are reported and their performance compared with four different treatments: baseline, a conventional 120°C low temperature bake for 48 h, and two mid-T bakes at 300°C and 400°C for 3 h. In addition, sample analysis using SEM, EDX and SIMS of witness samples is also shown. It is found that the mid-T bakes are not directly transferable to low frequency cavities. In the fundamental modes of the two test cavities, no performance gain over the baseline treatment nor a decreasing temperature dependent component with rising rf amplitude was observed. At frequencies above 1 GHz and low temperatures, the mid-T bakes show a reduced field dependence of RBCS compared to both the baseline and 120°C treatments.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2023.1259401</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2023.1259401</link>
        <title><![CDATA[Electromagnetic response of disordered superconducting cavities]]></title>
        <pubdate>2023-09-20T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Mehdi Zarea</author><author>Hikaru Ueki</author><author>J. A. Sauls</author>
        <description><![CDATA[We present the results for the resonant frequency shift and quality factor of disordered niobium (Nb) superconducting radio-frequency cavities driven out of equilibrium by the resonant microwave field. The theory is based on the non-equilibrium theory of superconductivity for the current response to the electromagnetic field at the vacuum–metal interface. We are able to accurately predict the observed frequency shifts with a precision of order fractions of kHz over the full temperature range 0 < T ≤ Tc, including the negative frequency shift anomalies that are observed very near Tc. The origin of these anomalies is shown to be the competition between the normal metal skin depth and the London penetration depth, which diverges as T→Tc−. An analytical approximation to the full current response, valid for |T − Tc|≪ Tc, accounts for the negative frequency shift near Tc. The non-monotonic dependence of the quality factor on the quasiparticle scattering rate is related to the pair-breaking effect of disorder on the superfluid fraction and, thus, the London penetration depth.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2023.1246016</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2023.1246016</link>
        <title><![CDATA[Superheating field in superconductors with nanostructured surfaces]]></title>
        <pubdate>2023-09-07T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>W. P. M. R. Pathirana</author><author>A. Gurevich</author>
        <description><![CDATA[We report calculations of a DC superheating field Hsh in superconductors with nanostructured surfaces. Numerical simulations of the Ginzburg–Landau (GL) equations were performed for a superconductor with an inhomogeneous impurity concentration, a thin superconducting layer on top of another superconductor, and superconductor–insulator–superconductor (S-I-S) multilayers. The superheating field was calculated taking into account the instability of the Meissner state with a non-zero wavelength along the surface, which is essential for the realistic values of the GL parameter κ. Simulations were performed for the material parameters of Nb and Nb3Sn at different values of κ and the mean free paths. We show that the impurity concentration profile at the surface and thicknesses of S-I-S multilayers can be optimized to enhance Hsh above the bulk superheating fields of both Nb and Nb3Sn. For example, an S-I-S structure with a 90-nm-thick Nb3Sn layer on Nb can boost the superheating field up to ≈500 mT, while protecting the superconducting radio-frequency (SRF) cavity from dendritic thermomagnetic avalanches caused by local penetration of vortices.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2023.1254302</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2023.1254302</link>
        <title><![CDATA[Spectral properties of a mixed singlet-triplet Ising superconductor]]></title>
        <pubdate>2023-09-01T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Sourabh Patil</author><author>Gaomin Tang</author><author>Wolfgang Belzig</author>
        <description><![CDATA[Conventional two-dimensional superconductivity is destroyed when the critical in-plane magnetic field exceeds the so-called Pauli limit. Some monolayer transition-metal dichalcogenides lack inversion symmetry and the strong spin-orbit coupling leads to a valley-dependent Zeeman-like spin splitting. The resulting spin-valley locking lifts the valley degeneracy and results in a strong enhancement of the in-plane critical magnetic field. In these systems, it was predicted that the density of states in an in-plane field exhibits distinct mirage gaps at finite energies of about the spin-orbit coupling strength, which arise from a coupling of the electron and hole bands at energy larger than the superconducting gap. In this study, we investigate the impact of a triplet pairing channel on the spectral properties, primarily the mirage gap and the superconducting gap, in the clean limit. Notably, in the presence of the triplet pairing channel, the mirage-gap width is reduced for the low magnetic fields. Furthermore, when the temperature is lower than the triplet critical temperature, the mirage gaps survive even in the strong-field limit due to the finite singlet and triplet order parameters. Our work provides insights into controlling and understanding the properties of spin-triplet Cooper pairs.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2023.1235918</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2023.1235918</link>
        <title><![CDATA[Characterization of dissipative regions of a N-doped superconducting radio-frequency cavity]]></title>
        <pubdate>2023-08-15T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>Eric M. Lechner</author><author>Basu Dev Oli</author><author>Junki Makita</author><author>Gianluigi Ciovati</author><author>Alex Gurevich</author><author>Maria Iavarone</author>
        <description><![CDATA[We report radio-frequency measurements of quality factors and temperature mapping of a nitrogen doped Nb superconducting RF cavity. Cavity cutouts of hot and cold spots were studied with low temperature scanning tunneling microscopy and spectroscopy, X-ray photoelectron spectroscopy and secondary electron microscopy. Temperature mapping revealed a substantial reduction of the residual resistance upon cooling the cavity with a greater temperature gradient and hysteretic losses at the quench location, pointing to trapped vortices as the dominant source of residual surface resistance. Analysis of the tunneling spectra in the framework of a proximity effect theory shows that hot spots have a reduced pair potential and a wider distribution of the contact resistance between the Nb and the top Nb oxide. Alone, these degraded superconducting properties account for a much weaker excess dissipation as compared with the vortex contribution. Based on the correlation between the quasiparticle density of states and temperature mapping, we suggest that degraded superconducting properties may facilitate vortex nucleation or settling of trapped flux during cooling the cavity through the critical temperature.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2022.934691</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2022.934691</link>
        <title><![CDATA[Is the optical conductivity of heavy fermion strange metals Planckian?]]></title>
        <pubdate>2023-01-25T00:00:00Z</pubdate>
        <category>Perspective</category>
        <author>Xinwei Li</author><author>Junichiro Kono</author><author>Qimiao Si</author><author>Silke Paschen</author>
        <description><![CDATA[Strange metal behavior appears across a variety of condensed matter settings and beyond, and achieving a universal understanding is an exciting prospect. The beyond-Landau quantum criticality of Kondo destruction has had considerable success in describing the behavior of strange metal heavy fermion compounds, and there is some evidence that the associated partial localization-delocalization nature can be generalized to diverse materials classes. Other potential overarching principles at play are also being explored. An intriguing proposal is that Planckian scattering, with a rate of kBT/ℏ, leads to the linear temperature dependence of the (dc) electrical resistivity, which is a hallmark of strange metal behavior. Here we extend a previously introduced analysis scheme based on the Drude description of the dc resistivity to optical conductivity data. When they are well described by a simple (ac) Drude model, the scattering rate can be directly extracted. This avoids the need to determine the ratio of charge carrier concentration to effective mass, which has complicated previous analyses based on the dc resistivity. However, we point out that strange metals typically exhibit strong deviations from Drude behavior, as exemplified by the “extreme” strange metal YbRh2Si2. This calls for alternative approaches, and we point to the power of strange metal dynamical (energy-over-temperature) scaling analyses for the inelastic part of the optical conductivity. If such scaling extends to the low-frequency limit, a strange metal relaxation rate can be estimated, and may ultimately be used to test whether strange metals relax in a Planckian manner.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2022.1120381</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2022.1120381</link>
        <title><![CDATA[Editorial: New heavy fermion superconductors]]></title>
        <pubdate>2023-01-09T00:00:00Z</pubdate>
        <category>Editorial</category>
        <author>Jeffrey W. Lynn</author><author>Vidya Madhavan</author><author>Lin Jiao</author>
        <description></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2022.1044620</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2022.1044620</link>
        <title><![CDATA[Evolution of magnetic properties in iron-based superconductor Eu-doped CaFe2As2]]></title>
        <pubdate>2022-12-13T00:00:00Z</pubdate>
        <category>Original Research</category>
        <author>K. Shrestha</author><author>L. Z. Deng</author><author>B. Lv</author><author>C. W. Chu</author>
        <description><![CDATA[This work presents the evolution of magnetic properties of EuxCa1−xFe2As2 (0 ≤ x ≤ 1, ECFA) samples. Unlike the resistivity data, that for magnetic susceptibility χ (T) does not show any clear evidence of the spin density wave (SDW) transition. When the Curie-Weiss contribution is subtracted, a weak anomaly appears at a temperature close to the SDW transition temperature (TSDW) determined from the resistivity data. To understand the magnetic orders arising from Fe-moments and Eu2+ spins order, we have studied the doping dependence of TSDW and Eu2+ antiferromagnetic order TN. It is found that TSDW increases almost linearly with increasing x and remains nearly unchanged above x ∼ 0.4, whereas TN first appears at x ∼ 0.4 and varies almost linearly with further increasing x. These observations suggest that magnetic orders due to two sublattices are coupled to each other. The results discussed here are helpful for understanding the magnetic properties of ECFA and other iron-based superconductors.]]></description>
      </item><item>
        <guid isPermaLink="true">https://www.frontiersin.org/articles/10.3389/femat.2022.944873</guid>
        <link>https://www.frontiersin.org/articles/10.3389/femat.2022.944873</link>
        <title><![CDATA[Multiple superconducting phases in heavy-fermion metals]]></title>
        <pubdate>2022-10-21T00:00:00Z</pubdate>
        <category>Review</category>
        <author>Emilian M. Nica</author><author>Sheng Ran</author><author>Lin Jiao</author><author>Qimiao Si</author>
        <description><![CDATA[Symmetry breaking beyond a global U(1) phase is the key signature of unconventional superconductors. As prototypical strongly correlated materials, heavy-fermion metals provide ideal platforms for realizing unconventional superconductivity. In this article, we review heavy-fermion superconductivity, with a focus on those materials with multiple superconducting phases. In this context, we highlight the role of orbital-selective (matrix) pairing functions, which are defined as matrices in the space of effective orbital degrees of freedom such as electronic orbitals and sublattices as well as equivalent descriptions in terms of intra- and inter-band pairing components in the band basis. The role of quantum criticality and the associated strange-metal physics in the development of unconventional superconductivity is emphasized throughout. We discuss in some detail the recent experimental observations and theoretical perspectives in the illustrative cases of UTe2, CeRh2As2, and CeCu2Si2, where applied magnetic fields or pressure induce a variety of superconducting phases. We close by providing a brief overview of overarching issues and implications for possible future directions.]]></description>
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