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Physics Condensed Matter Superconductivity

cond-mat.supr-con Watch Superconductivity

Thursday 6 August

Superconductivity · Cross-listed from cond-mat.mes-hall

Theory of spin-wave transport in ferromagnet-superconductor heterostructures: Negative refraction, perfect imaging and temperature-controlled spin-wave optics

Tomas T. Osterholt, Thijs van der Meer, Pim H. Vree et al. (+4 more)

We investigate spin-wave transport in ferromagnetic insulator-superconductor (FMI-SC) heterostructures and develop a general theoretical framework for spin-wave optics in these hybrid systems. We demonstrate that Meissner screening by the superconductor gives rise to a range of unconventional wave phenomena, including negative phase- and group-velocity refraction, and reflection and refraction laws that differ fundamentally from their optical counterparts. Within this framework, we derive the spin-wave Fresnel equations governing reflection and transmission at FMI-SC interfaces and show that the scattering properties exhibit a pronounced temperature dependence, enabling tunable spin-wave mirrors and refractive elements. Most strikingly, we find that superconducting screening can produce nearly straight isofrequency contours, far flatter than the kinked, intrinsically curved contours attainable in conventional dipolar spin-wave systems. We show that these straight contours enable functionalities such as perfect spin-wave imaging, efficient waveguiding, and interferometric elements, such as phase shifters and beam splitters, with unconventional properties. Our results establish FMI-SC heterostructures as a versatile platform for temperature-tunable spin-wave optics and interferometric magnonic devices.
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All authors Tomas T. Osterholt, Thijs van der Meer, Pim H. Vree, Merel A. Bouma, Michael Borst, Toeno van der Sar, Rembert A. Duine

Superconductivity · Cross-listed from quant-ph

Quantum error correction with global control

Roberto Menta, Lindsay Bassman Oftelie, Ashkan Abedi et al. (+5 more)

Reaching fault tolerance means scaling qubit counts by orders of magnitude, a jump that conventional superconducting architectures cannot sustain without solving the so-called `wiring problem'. Global control sidesteps this bottleneck, but implementing quantum error correction (QEC) on previously proposed global architectures incurs extremely steep overhead costs, due to the need for separate correction procedures for the computational and auxiliary qubits that comprise the global device. We resolve this by introducing the first globally-controlled architecture with zero qubit overhead. Every physical qubit is a computational qubit, and thus, every qubit is protected under a single error correcting scheme. We identify a class of cyclic stabilizer codes realizable through global iSWAP and single-qubit gates, yielding QEC thresholds nearly seven orders of magnitude larger than previous estimates for globally-controlled arrays. We further show these thresholds improve systematically as the global architecture is augmented with a limited amount of local measurement sites, demonstrating a trade-off between wiring simplicity and fault-tolerant performance.
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All authors Roberto Menta, Lindsay Bassman Oftelie, Ashkan Abedi, Francesco Cioni, Marco Polini, Seth Lloyd, Francesco Caravelli, Vittorio Giovannetti

Superconductivity

Annular Majorana mode in a superconducting topological insulator

Shengshan Qin, Chi Wu, Lun-hui Hu et al. (+2 more)

When the surface states of a topological insulator becomes superconducting, topological superconductivity can be obtained, and each vortex on the surface can host one single Majorana zero-energy mode which is usually a wave packet decaying exponentially off the vortex core. Here, we predict stable Majorana zero-energy mode whose wave function is ring-shape, dubbed as annular Majorana mode, in the superconducting vortex in topological insulators respecting $3$-fold or $6$-fold rotational symmetry. Such topological insulators are featured with a single nonlinear Dirac cone located at $\bar{\Gamma}$ or three linear Dirac cones at $\bar{\text{M}}$ in the surface Brillouin zone. The annular Majorana mode originates from the effective chiral $f$-wave superconductivity on the nonlinear Dirac cone in the former case and the interference of the effective chiral $p$-wave superconductivity on the three linear Dirac cones in the latter. In both cases, the annular Majorana mode is stabilized by the rotational symmetry and the winding number $3$ carried by the surface states. Candidate materials supporting the annular Majorana mode are predicted. Our work provides new insights into the topological superconductivity in superconducting topological insulators.
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All authors Shengshan Qin, Chi Wu, Lun-hui Hu, Tiantian Zhang, Jiangping Hu

Wednesday 5 August

Superconductivity

Kinetic Lifshitz invariants and dynamics of nonreciprocal fluctuations in superconductors

Tony Liu, Joaquim Telles de Miranda, Daniel Shaffer et al. (+1 more)

We derive the generalized time-dependent Ginzburg-Landau theory of a disordered noncentrosymmetric superconductor from the Keldysh nonlinear sigma model, using a two-dimensional electron gas with Rashba spin-orbit coupling and an in-plane Zeeman field as a minimal model. On the thermodynamic side we construct the Lifshitz invariants of the free energy, the linear and cubic gradient terms and the momentum-odd part of the quartic vertex, and trace their dependence on disorder. These couplings are governed by a single closed-form kernel controlled by the ratio of the Dyakonov-Perel spin-relaxation rate to temperature, interpolating between the weak-relaxation regime, where the invariants are suppressed, and the relaxation-dominated regime, where the helical modulation of the order parameter saturates at a universal, disorder-independent value. This crossover reconciles conflicting results for the magnetoelectric couplings of dirty Rashba superconductors. Because the theory is formulated on the Keldysh contour, it also determines the dissipative dynamics: the relaxation rate of a fluctuation with pair momentum $\mathbf{q}$, and hence, by the fluctuation-dissipation theorem, the Langevin noise power, acquires a term odd in $\mathbf{q}$ and odd in the magnetic field. The structure of this kinetic Lifshitz invariant is dictated by Onsager reciprocity: friction and noise renormalize in lockstep, so equal-time fluctuations remain Gibbsian while the dynamics are nonreciprocal. As applications we compute the superconducting diode efficiency near $T_c$, where the cubic invariant competes with the quartic vertex and with even higher-gradient terms rendered odd by the helical shift, reversing the sign of the diode coefficient, and the fluctuation-induced magnetochiral anisotropy above $T_c$, where the current-resolved nonreciprocal resistance forms a plateau across the Gaussian regime.
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All authors Tony Liu, Joaquim Telles de Miranda, Daniel Shaffer, Alex Levchenko

Superconductivity · Cross-listed from cond-mat.str-el

Superconducting and charge-ordered phases from Dirac quantum spin liquids on the triangular lattice

Andreas Feuerpfeil, Ronny Thomale, Subir Sachdev et al. (+1 more)

Triangular-lattice quantum spin-liquid insulators are observed to undergo transitions to superconductivity under pressure or doping, and exhibit enhanced terahertz conductivity when driven by mid-infrared light. We present a general theoretical framework for the emergence of superconducting and charge-ordered phases from a U(1) Dirac spin liquid with fermionic spinons, as well as from its gapped $\mathbb{Z}_2$ and chiral descendants. Numerical studies have provided substantial evidence for these spin-liquid states. The spin-liquid phase hosts fractionalized Dirac spinons coupled to an emergent gauge field, whereas the superconducting and charge-ordered phases are conventional, with neither fractionalized excitations nor emergent gauge dynamics. The transition between these phases is driven by the Higgs condensation of spinless charge-$e$ bosonic chargons (“doublons” and “holons”). We show that the projective symmetry group of the Dirac spinons uniquely determines the symmetry and dispersion of the chargons, allowing us to construct an effective low-energy theory near the chargon band minima. Gauge-invariant composites of the chargon Higgs fields provide the order parameters characterizing the phases. The resulting phase diagram contains a rich variety of ordered states, including $d+id$ superconductivity, charge-density waves, bond-density waves, and pair-density waves.
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All authors Andreas Feuerpfeil, Ronny Thomale, Subir Sachdev, Pietro M. Bonetti

Superconductivity

Nonlinear nanoelectromechanics of a movable Cooper-pair box

S. Park, A. Patra, L. Y. Gorelik et al. (+3 more)

We theoretically study the dynamics of a movable Cooper-pair box coupled to a normal-metal pillar using a semiclassical approach. We analyze the dynamical stability induced by the nonlinear nanoelectromechanical coupling between the mechanical motion and an inelastic Andreev tunneling through linear stability and bifurcation analyses. As a function of $\eta$, defined as the ratio of electrostatic energy to Josephson coupling energy, the system exhibits reentrant stability. At small $\eta$, the fixed point loses stability through a supercritical Hopf bifurcation, giving rise to self-sustained vibrations. With a further increase of $\eta$, a second critical point appears, at which the fixed point regains stability. We show that this second transition corresponds to an inverse subcritical Hopf bifurcation in the adiabatic regime and to an inverse supercritical Hopf bifurcation in the nonadiabatic regime. These results extend previous studies of adiabatic self-vibrations to the nonadiabatic regime and reveal a rich nonlinear dynamical phase diagram arising from the interplay between electronic and mechanical degrees of freedom in superconducting devices.
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All authors S. Park, A. Patra, L. Y. Gorelik, M. J. Park, H. C. Park, R. I. Shekhter

Superconductivity · Cross-listed from cond-mat.str-el

Ghost-RISB for Correlated Electron-Phonon Systems: Application to the Hubbard-Holstein Model

Samuele Giuli, Ricardo J. Campos-Lopes, Emin Moghadas et al. (+1 more)

We develop a generalization of the ghost-rotationally-invariant slave-boson (ghost-RISB) method that incorporates local phonon modes coupled to arbitrary on-site electronic degrees of freedom, enabling a nonperturbative treatment of electron-electron and electron-phonon interactions within an efficient variational framework. The method extends the ghost-orbital construction to capture dynamical self-energy effects and phonon-induced renormalizations beyond static slave-boson approaches. Benchmarking against dynamical mean-field theory (DMFT) results for the Hubbard-Holstein model, we find excellent quantitative agreement for electron quasiparticle weights and phonon properties across a wide range of coupling strengths, and it captures accurately the competition between electron-electron and electron-phonon interactions. We show that the inclusion of the ghost orbitals is crucial to accurately describe the regime of low-frequency, strongly dynamical, phonons. The extended ghost-RISB achieves this accuracy at a fraction of the computational cost of DMFT, due to its self-consistency rooted in static observables instead of dynamical ones, enabling rapid exploration of correlated electron-phonon phase diagrams. We exploit this advantage to characterize the most demanding regime of strong coupling and adiabatic phonons. Our analysis shows a suppression of the superconducting order parameter, which is interpreted as a Franck-Condon-like reduction of the overlap between the phonon wavefunctions associated with empty and doubly-occupied sites in the bipolaronic regime.
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All authors Samuele Giuli, Ricardo J. Campos-Lopes, Emin Moghadas, Massimo Capone

Superconductivity

In search of novel ductile superconductors

Yiming Zhang and Samuel Poncé

We performed a first-principles high-throughput screening of the mechanical properties of phonon-mediated superconductors selected from the recent experimentally synthesized superconducting materials database PRX Energy 4, 033012 (2025). We developed the workflows that combine first-principles calculations of elastic constants and generalized stacking fault energies to assess the ductility of superconducting candidates. Starting from the 250 materials identified with promising superconducting critical temperatures, we computed their elastic tensors to evaluate bulk and shear moduli, Pugh's ratio, and Pettifor's ratio from first principles. To further characterize their plastic deformation behavior, we calculated the stacking fault energy and surface energy for selected materials and slip directions, allowing the estimation of Rice's ratio and ductility indicators. We found that several new materials simultaneously exhibit high-T$_c$ and ductility including HfPd$_2$Al, TiRuSb, and ZrNi$_2$Ga with predicted isotropic T$_c$= 6.80K, 12.88K, and 8.23K, respectively. This work offers a quantitative mapping of mechanical performance across a wide range of superconductors and provides a reference to identify new mechanically promising superconductors.
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Superconductivity

Microscopic theory of the field-induced instability of the vortex-free state in superconducting thin-film strips

Takayuki Kubo

In the Pearl–London theory, the edge-barrier-disappearance field of a superconducting thin-film strip depends on an arbitrary short-distance core cutoff because the vortex is treated as a point object. The theory does not determine the cutoff or how it depends on temperature $T$, and therefore cannot determine the $T$ dependence of the instability field. Here we formulate the microscopic stability problem directly for the vortex-free superconducting state. This removes the core-cutoff ambiguity and determines the instability field $B_s$ over the full temperature range and across all width regimes considered here. For a homogeneous dirty strip with negligible self-field, three width regimes occur. For $W<W_1(T)$, superconductivity disappears continuously into the normal state through a one-dimensional (1D) instability. For $W_1(T)<W<W_2(T)$, an edge-selective two-dimensional (2D) long-wavelength mode becomes unstable. For $W>W_2(T)$, the critical wave number is finite and the unstable mode is localized near an edge. In the wide-strip limit, $B_s\propto1/W$, recovering the Pearl–London scaling. In sufficiently narrow strips, however, the Pearl–London edge-barrier picture fails qualitatively.
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Tuesday 4 August

Superconductivity

Thermodynamic phase transition, pairing symmetry and Fermi surface topology in Ruddlesden-Popper nickelate films

Yu Miao, Zhiwei Wang, Hongxu Sun et al. (+9 more)

Ruddlesden-Popper (RP) nickelates provide an uncharted territory to explore high-transition-temperature (high-$T_C$) superconductivity and superconducting mechanism. Here, we investigate the electronic structure of a new type of high-$T_C$ superconducting RP nickelate heterostructure $\mathrm{La_2PrNi_2O_7/NdAlO_3}$ by angle-resolved photoemission spectroscopy. A superconducting state is observed without a pseudogap state, enabling a direct measurement of the superconducting order parameter and a microscopic extraction of the electronic specific heat. The observed superconducting gap opens at $T_C$ with prominent coherence peaks, illustrating the emergence of nonzero order parameter upon entering the superconducting state. An electronic specific heat jump appears at $T_C$, further demonstrating a thermodynamic phase transition. The magnitude of the superconducting order parameter is quantified by the observed superconducting coherence peaks, and a nodeless behavior is unambiguously established in the absence of pseudogap. The underlying Fermi surface consists of $\alpha$, $\beta$ and $\gamma$ pockets, exhibiting a multi-orbital nature. Strain dependent measurements further reveal the $\gamma$ pocket in all superconducting and non-superconducting films with different epitaxial strain. Our results establish the missing thermodynamic evidence for superconducting phase transition in nickelates. They also provide direct evidence for the symmetry of the superconducting order parameter and illustrate the relationship between Fermi surface topology and the emergence of superconductivity in RP nickelate films.
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All authors Yu Miao, Zhiwei Wang, Hongxu Sun, Jianchang Shen, Runqing Luan, Zhipeng Ou, Xinru Yong, Zhenyu Wang, Tao Wu, Haoyu Hu, Junfeng He, Xianhui Chen

Superconductivity · Cross-listed from cond-mat.mes-hall

Surface-Selective Probe of Spin-Triplet Superconductivity in Rhombohedral Graphene

Kilian Krötzsch, Zekang Zhou, Kryštof Kolář et al. (+6 more)

Superconductivity in rhombohedral graphene has been observed across many layer numbers, with mounting evidence pointing toward spin-triplet pairing, yet complementary probes of the superconducting spin structure remain needed. Here we use one-sided WS$_2$ proximity in rhombohedral pentalayer graphene (R5G) as a surface-selective spin-orbit probe. The induced Ising spin-orbit coupling is strongest for carriers localized near the WS$_2$ interface, allowing the displacement field to tune the overlap between superconducting carriers and the spin-orbit perturbation. We observe a strongly asymmetric superconducting landscape: two robust pockets, SC1 and SC2, survive only on mutually opposite signs of displacement field, while a third pocket, SC3, is substantially weaker. Gate-tracking features, quantum oscillations, and self-consistent band-structure calculations identify the layer polarization and Fermi-surface character of the relevant carriers. The robust superconducting states are absent or strongly weakened when the active high-DOS carriers are polarized toward the WS$_2$ interface. Since Ising spin-orbit coupling is compatible with time-reversed spin-singlet pairing but competes with same-spin intervalley triplet pairing by canting or pinning the parent spin texture, this surface-selective suppression provides additional evidence for spin-triplet superconductivity involving both hole-like and electron-like carriers. Our results establish one-sided TMD proximity as a displacement-field-tunable probe of superconducting spin structure in rhombohedral graphene.
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All authors Kilian Krötzsch, Zekang Zhou, Kryštof Kolář, Yonggen Li, Kenji Watanabe, Takashi Taniguchi, Moty Heiblum, Cyprian Lewandowski, Mitali Banerjee

Superconductivity

Two-phonon pairing and superconductivity in $SrTiO_3$

Antonio Santacesaria, Cristiano Muzzi, Maria Eleonora Temperini et al. (+3 more)

We explore the possibility that the two-phonon pairing mechanism proposed by Ngai can explain superconductivity in doped strontium titanate (STO). The two-phonon deformation potential is evaluated using two distinct theoretical estimates based on first-principles calculations and two empirical estimates based on experimental data, yielding very large values of the same order of magnitude. We derive the effective electron-electron interaction mediated by two-phonon exchange. Crucial to our computations is the strong dispersion of the involved soft phonons. Because the scale of the two-phonon interaction is much larger than the Fermi energy, the Migdal theorem does not apply. We obtain a one-loop Eliashberg equation that can be solved in the weak-coupling limit. We find that despite the significant electron-phonon matrix element, phase space considerations considerably reduce the effective coupling. A two-phonon mechanism can not be excluded based on the $T_c$ magnitude, but its value is dominated by the high-energy-frequency physics and is weakly affected by the soft-phonon behavior. The theory predicts a $T_c$ that monotonously increases with doping, which is not in accordance with the experiment. We identify the conditions for a two-phonon mechanism to be effective in other materials and discuss possible candidates.
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All authors Antonio Santacesaria, Cristiano Muzzi, Maria Eleonora Temperini, Paolo Barone, Maria N. Gastiasoro, José Lorenzana

Superconductivity

Pressure induced magnetic-field-free superconducting diode effect in NbSe2 flake

Shihao Zhu, Tian Le, Cuiying Pei et al. (+17 more)

The superconducting diode effect (SDE) is a fascinating nonreciprocal phenomenon where the critical current is different for opposite current directions. It is widely believed that realizing SDE requires breaking both inversion symmetry (IS) and time-reversal symmetry (TRS), which are usually achieved via heterostructure engineering and applying external magnetic fields. Here, we report a pressure-induced magnetic-field-free SDE in NbSe2 flakes without any heterostructures. We show that pressure alone breaks the IS, as confirmed by the second harmonic generation. Crucially, upon applying an out-of-plane magnetic field (B), the SDE exhibits even-in-B behavior, implying the absence of explicit TRS breaking. This finding challenges the prevailing theoretical paradigm and demonstrates that a magnetic-field-free SDE can emerge without explicitly breaking TRS. Thereby, our work establishes pressure engineering as a powerful tool for inducing nonreciprocal superconductivity and designing versatile, magnetic-field-free superconducting devices.
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All authors Shihao Zhu, Tian Le, Cuiying Pei, Changhua Li, Yi Liao, Yi Zhao, Lingxiao Zhao, Qi Wang, Juefei Wu, Qilian Zhang, Yueshen Wu, Tonghuan Fu, Xujie Lü, Wenge Yang, Jie Shen, Jun Li, Yulin Chen, Xiao Lin, Wen-Yu He, Yanpeng Qi

Superconductivity

Pressure-induced Superconductivity in Thermoelectric Semiconductor Mg3Sb2

Cuiying Pei, Yasong Wu, Airan Li et al. (+14 more)

The intrinsic electronic structures of narrow bandgap thermoelectric (TE) materials serve as a platform for the investigation of coupling effects of quasi-particles under high pressure, enabling the exploration of emerging electronic and phonon transport, superconductivity, and topological transition. Here, we report the discovery of pressure-induced superconductivity in the TE semiconductor Mg3Sb2. Upon the increased pressure, the metallization occurs at 8.7 GPa, followed by a superconducting transition concomitant with a carrier-type crossover from p- to n-type. This phenomenon arises from a pressure-induced structural phase transition from the semiconducting P-3m1 to the metallic C2/m-I phase. The superconducting critical temperature (Tc) exhibits a dome-shaped pressure dependence, peaking at 3.3 K at 12.6 GPa. Combined theoretical calculations, high-pressure Raman spectroscopy, and X-ray diffraction (XRD) measurements reveal an additional structural transition above 20 GPa, yielding a distinct C2/m-II phase. Our findings establish the high-pressure phase diagram of Mg3Sb2, elucidate its pressure-dependent electronic properties, and provide valuable insights for future investigations of TE materials under high pressure.
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All authors Cuiying Pei, Yasong Wu, Airan Li, Juefei Wu, Qi Wang, Yifan Zhu, Yi Zhao, Lingling Gao, Changhua Li, Weizheng Cao, Shihao Zhu, Mingxin Zhang, Yulin Chen, Chenguang Fu, Tiejun Zhu, Jiong Yang, Yanpeng Qi

Superconductivity · Cross-listed from cond-mat.str-el

Exotic superconductivity in the doped Kitaev quantum spin liquid

Takahiro Misawa and Kota Ido

We investigate superconductivity in a doped Kitaev quantum spin liquid by applying the many-variable variational Monte Carlo method to the hole-doped $t$-$J$-type Kitaev model. Using a projected pair-product wave function that can exactly represent the Kitaev quantum spin liquid, we examine the stability of superconducting phases on isotropic two-dimensional clusters. For the ferromagnetic Kitaev interaction, robust triplet $p$-wave superconductivity coexists with ferromagnetism in the low-to-intermediate doping regime but is suppressed as the system approaches the fully polarized ferromagnetic phase. For the antiferromagnetic Kitaev interaction, superconductivity exhibits a change in the dominant pairing symmetry from spin-dependent triplet $p$-wave at low doping to singlet $d+id$ at intermediate doping. By varying the strength of the ferromagnetic Kitaev interaction at fixed doping, we show that the triplet superconductivity increases together with the ferromagnetic moment and becomes strongest slightly below full polarization. Our results provide a theoretical basis for experimental searches for unconventional superconductivity, such as triplet superconductivity coexisting with ferromagnetism, in carrier-doped Kitaev candidate materials.
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Monday 3 August

Superconductivity · Cross-listed from cond-mat.str-el

Large scale neural quantum states reveal the interplay between superconductivity and quantum criticality in the Hofstadter-Hubbard model

Christopher Roth, Andrew Millis and Tomohiro Soejima

Understanding how a parent insulating state shapes the superconductivity that emerges upon doping is a long-standing problem dating back to Anderson's resonating-valence-bond proposal. The triangular-lattice Hofstadter-Hubbard model with $\pi/2$ flux per plaquette offers an ideal setting: at half filling it hosts two distinct parent states—an integer quantum Hall insulator and a chiral spin liquid—separated by a topological phase transition. Using neural quantum states on tori of up to $432$ sites, we present strong evidence that the transition is continuous, with a vanishing $2e$ charge gap and critical charge fluctuations. Upon doping, we find a topological superconductor on either side of the transition. While the pairing order parameter remains nearly unchanged across the transition, the superfluid stiffness is strongly enhanced near the critical point. The energy scale of the superconductor is therefore set not by which parent state is doped, but by proximity to the transition between them. Our results establish neural quantum states as a powerful tool for understanding the interplay between unconventional electronic correlations and superconductivity.
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Superconductivity · Cross-listed from cond-mat.str-el

Spin-charge separation in the triangular-lattice Hofstadter-Hubbard model

Yuntian Gu, Hui Yang, Zhehao Dai et al. (+1 more)

Recent experiments in moiré materials have enabled the realization of a variety of exotic quantum phases. In this context, the Hofstadter-Hubbard model has been proposed as a possible setting for hosting chiral spin liquid. Concurrently, significant progress has been recently made in the computational methods for two-dimensional many-body fermion systems, which makes numerically studying this challenging model a real possibility in genuine 2D geometry. Motivated by these advances, we investigate the putative chiral spin liquid phase in the triangular-lattice Hofstadter-Hubbard model using variational Monte Carlo with neural quantum states (NQS) and projected entangled pair states (PEPS). We observe spin-charge separation directly in real space through numerical spin-pumping simulation and real-time spin and charge motion. In addition, in the context of anyonic superconductivity conjectured in this model, we find a positive two-electron binding energy on small systems, but it decreases below our numerical resolution as the system size increases. Our work demonstrates NQS and PEPS as powerful tools, capable of cross-checking each other, for diagnosing topological order and fractionalized excitations in strongly correlated electronic systems.
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All authors Yuntian Gu, Hui Yang, Zhehao Dai, Yantao Wu

Superconductivity

Superconducting dome due to the Fano-Feshbach shape resonance in artificial high-Tc superlattices

Gaetano Campi, Andrea Alimenti, Danielle Villa et al. (+7 more)

In this work we provide compelling experimental validation of the Bianconi Perali Valletta (BPV) theory predicting a superconducting dome based on a quantum material design of Artificial High TC Superlattices (AHTS) made with a selected nanoscale heterostructure geometry. These AHTS are SNSN superlattices of quantum wells of period d, composed of first units, superconducting doped Mott insulator layers with Rashba spin orbit coupling (S) of thickness L, intercalated by second units, normal metal spacers (N). In these superlattices, grown by molecular beam epitaxy (MBE), the experimental superconducting dome is obtained by material quantum design changing the chemical potential via the quantum geometrical factor L/d which tunes the Fano-Feshbach shape resonance in the pair transfer between superconducting gaps in the BCS regime and different gaps in the BEC-BCS crossover. Here we present a systematic magneto-transport study of AHTS artificial superlattices across the full doping range of the superconducting dome, from the deeply underdoped to the overdoped regime, using pulsed magnetic fields up to 72 T. By varying the L/d ratio, we tune the effective hole concentration delta=0.45(1-L/d) and map the evolution of the resistive transitions, the upper critical magnetic field and the Ginzburg-Landau coherence length
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All authors Gaetano Campi, Andrea Alimenti, Danielle Villa, G. Alexander Smith, Fedor F. Balakirev, Luis Balicas, Andrea Perali, Sergio Caprara, Gennady Logvenov, Antonio Bianconi1

Superconductivity

Composite quantum geometry of superconductors

Florian Simon, Thomas Bernat and Annica M. Black-Schaffer

The interplay of superconductivity and the quantum geometry of the normal state has recently been the subject of an array of studies, especially regarding the superfluid weight. In this work, we turn our attention to the quantum geometry of the superconducting state itself, set by the Bogoliubov-de Gennes (BdG) Hamiltonian, which dictates the geometric and topological properties of superconductivity. We show that under three general conditions, namely superconducting fitness, orbital uniformity of the superconducting pairing, and absence of normal-state spin-flip terms, the BdG quantum geometry exactly separates into a sum of the normal-state quantum geometry and an additional pairing quantum geometry, thereby displaying a simple composite structure. We show that this separation holds for all spin-singlet and -triplet pairings, including nonunitary spin-triplet pairing. We further provide explicit analytical formulas for the pairing quantum geometry for all these cases. These results establish how superconducting pairing alone easily drives both topology and a finite quantum metric, thus being present even in topological trivial or flat band superconductors, with no normal state quantum geometry. To complement these results, we also derive the BdG quantum geometry of a general two-orbital spin-singlet superconductor with non-uniform pairing and finite superconducting fitness. Here, our explicit analytical results establish a non-separable composite BdG quantum geometry, with the normal state and pairing contributions generally intertwining, thereby producing even more possibilities for finite quantum geometry. Our results provide design rules for creating superconductors and superconducting hybrid structures with nontrivial topology and finite quantum metric and will additionally help in the experimental diagnosis of unconventional superconductivity.
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Superconductivity

Screening phonon-mediated superconductors from static orbital Hamiltonians

Jian-Feng Zhang, Ze-Feng Gao, Xiao-Qi Han et al. (+6 more)

The first-principles search for superconductors is severely limited by the high cost of electron-phonon coupling (EPC) calculations. Here we develop a low-cost, physically transparent framework that identifies strong-EPC materials directly from static orbital-based Hamiltonians without explicit phonon perturbation calculations. Verification using density functional perturbation theory (DFPT) for representative superconductors shows that the framework captures semi-quantitatively the EPC scale at substantially lower computational cost. Applied to more than 36,000 compounds in the MattKeyBond database, it identifies 34 dynamically stable superconducting candidates with calculated $T_c > 10$ K after DFPT verification. These candidates reveal two distinct routes to relatively high-$T_c$ superconductivity: a metallized covalent $\sigma$-bond route that is more favorable for achieving high-$T_c$ superconductors, and a Fermi-level density-of-states accumulation route that can enhance $T_c$ but usually to a more limited extent.
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All authors Jian-Feng Zhang, Ze-Feng Gao, Xiao-Qi Han, Dingshun Lv, Miao Gao, Kai Liu, Xinguo Ren, Zhong-Yi Lu, Tao Xiang

Superconductivity

Emergence of Double-Dome Superconductivity in the Pressurized Dirac Semimetal BaMg2Bi2

Qi Wang, Juefei Wu, Cuiying Pei et al. (+3 more)

Dirac semimetal BaMg2Bi2 is reported to be a unique topological material that manifests surface superconductivity that coexistswith bulk band topology at ambient pressure. Here, we present a comprehensive investigation of high-pressure superconductingproperties in BaMg2Bi2 single crystal. Significantly, a pressure-driven double-dome superconducting behavior was revealed, withthe superconducting transition temperature Tc approaching the maximum values of 6.67 K at 4.5 GPa and 7.22 K at 10.4 GPafor the first and second superconducting domes, respectively. The combination of high-pressure X-ray diffraction, Hall resistivitymeasurements, and theoretical calculations demonstrates that, the first superconducting regime is closely related to the pressure-modulated Lifshitz transition, whereas the second superconducting phase emerges concurrently with a structural transition fromthe ambient-pressure P3m1 phase to a high-pressure Pnma phase.
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All authors Qi Wang, Juefei Wu, Cuiying Pei, Yi Zhao, Yiyan Wang, Yanpeng Qi

Superconductivity

Superconducting ternary compounds Li-X-B (X=Mo, W) within the mild pressure range: First-principles predictions

Bangshuai Zhu, Juefei Wu, Dexi Shao et al. (+6 more)

Among the superconducting hydrides under high pressure, a number of studies concentrate on the ternary compounds to explore unique superconductors, which are capable of reducing the stable pressure and maintain superconductivity. In this work, to verify our proposed strategy of ternary composition lines (TCLs) to explore ternary compounds, we combined the first-principles calculations and crystal structure predictions to study the ternary compounds Li-X-B (X=Mo, W) under high pressure. After calculations along five and four TCLs in Li-W-B and Li-Mo-B, respectively, five Li-W-B compounds and four Li-Mo-B compounds were predicted. The compositions of LiWB4, Li4MoB2 and LiMo2B2 could be thermodynamically stable under high pressure, and Li2WB6 is around 0.02 eV/atom above the convex hull at 0 GPa, which has potential for synthesizing. Both of the predicted Li2WB6 P6/mmm and Li2WB4 R-3m are superconducting and their Tc are around 11 K, which are similar to the Tc of WB2 P6/mmm around 100 GPa. An anomalous increase of Tc was found in Li4MoB2 C2/m upon compression. We carried out full ternary search (FTS) to evaluate the validity of the TCLs strategy in Li-W-B system at 0 GPa. Our results are helpful for understanding the phase diagram of Li-X-B (X=Mo, W) under high pressure and the introducing of Li atoms provide candidate structures to reduce the measured stable pressure from ~100 GPa in WB2 P6/mmm to 0 GPa. Meanwhile, we preliminary validate the strategy of TCLs in structure predictions and we expect to improve this strategy in the future, shedding light on the studies of ternary compounds.
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All authors Bangshuai Zhu, Juefei Wu, Dexi Shao, Junjie Wang, Yu Han, Cuiying Pei, Qi Wang, Jian Sun, Yanpeng Qi

Superconductivity

Cryogenic focused-ion-beam microstructuring enabling quantitative $c$-axis transport measurements in Tl$_2$Ba$_2$CuO$_{6+\delta}$

Ayanesh Maiti, Carsten Putzke, Linus Holeschovsky et al. (+10 more)

Absolute transport measurements in correlated quantum materials are often limited by disorder, inhomogeneity, geometric uncertainty, and small crystal size. Focused ion beam (FIB) technology offers a route to overcome many of these limitations by enabling transport devices with precisely defined geometry to be fabricated from lamellae extracted from carefully selected regions of a crystal, but its application to cuprate superconductors has been hindered by ion-beam-induced damage. Here we study the clean overdoped cuprate Tl2201 and show that conventional FIB processing causes thermally driven oxygen loss, while cryogenic FIB microstructuring largely suppresses this degradation and preserves the crystal structure from the bulk to the atomic scale. Microstructured devices quantitatively reproduce established in-plane resistivity and Hall carrier density measurements without rescaling. Applying this approach to $c$-axis transport, we obtain absolute $\rho_c(T)$ values approximately three times larger than previously reported, bringing the transport anisotropy into quantitative agreement with the known Fermi surface geometry within an isotropic relaxation-time approximation. These results resolve a long-standing discrepancy between transport and quantum oscillation measurements in overdoped Tl2201 and establish cryogenic FIB microstructuring as a route to reliable quantitative transport measurements in quantum materials where disorder, inhomogeneity, geometry, or small crystal size have previously limited experimental accuracy.
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All authors Ayanesh Maiti, Carsten Putzke, Linus Holeschovsky, Roemer D. H. Hinlopen, Chunyu Guo, Dorothee Herrmann, Seunghyun Khim, Berit H. Goodge, Andre W. Tyler, Michele S. Conroy, Andreas W. Rost, Andrew P. Mackenzie, Philip J. W. Moll

Superconductivity

Pressure-induced concurrent amorphization and superconductivity in topological material NbNiTe5

Lingxiao Zhao, Yi Zhao, Bangshuai Zhu et al. (+6 more)

We have systematically studied the structural and electronic properties of a topological material NbNiTe5 under high pressure. The evolution of the normal state resistance shows a non-monotonic trend from 0.7 GPa to 5.1 GPa, in accordance with the second-order transition along the inter-layer direction observed in X-ray diffraction and Raman spectra. At around 10 GPa, the sample starts amorphization, which is concurrent with the emergence of superconductivity. Upon further compression, the structural disorder enhances and the superconducting transition becomes clearer, suggesting that the superconductivity is modulated by the degree of disorder in NbNiTe5 under high pressure. Within 45.7 GPa, the superconducting transition temperature (Tc) slowly rises from 0.6 K at 9.5 GPa to 1.4 K at 45.7 GPa. Our findings extend the family of transition metal chalcogenide superconductors and shed new light on understanding superconductivity in disordered systems.
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All authors Lingxiao Zhao, Yi Zhao, Bangshuai Zhu, Qi Wang, Cuiying Pei, Juefei Wu, Jin-Ke Bao, Wen-He Jiao, Yanpeng Qi

Superconductivity

Enhanced and robust superconductivity in La0.8Sr0.2NiO2 membranes compressed up to 210 GPa

Shu Cai, Yuqing Tian, Shengjun Yan et al. (+10 more)

The discovery of superconductivity in infinite-layer nickelate thin films has opened a new frontier for exploring unconventional oxide superconductors beyond the copper oxide family. However, the presence of substrate hampers investigations under very high pressure. Recently, this problem was circumvented by a study of freestanding Nd0.85Sr0.15NiO2 membranes, which revealed that superconducting transition temperature kept increasing as the pressure was ramped up to 91 GPa, without showing signs of saturation. Naturally, one wonders what would happen at even higher pressures. Here, we report that superconductivity in a freestanding La0.8Sr0.2NiO2 membrane persists under applied ultrahigh pressures up to 210 GPa. The superconducting transition onset temperature exhibits a continuous dome-like evolution, increasing from 16 K at ambient pressure to a peak of 74.5 K at 146 GPa, and then gradually decreasing to 57.4 K at 210 GPa. Such robustness of superconductivity against ultrahigh pressure has not been observed in high-Tc oxide superconductors before.
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All authors Shu Cai, Yuqing Tian, Shengjun Yan, Jinyu Zhao, Bo Hao, Jianfeng Zhang, Shuaihang Sun, Yang Ding, Qi Wu, Ho-kwang Mao, I. Bozovic, Yuefeng Nie, Liling Sun

Superconductivity

Spin Josephson diode effect induced by higher-harmonic spin Josephson currents in a diffusive Josephson junction

Shin-ichi Hikino

We theoretically investigate the spin Josephson diode effect (SJDE) in a diffusive Josephson junction with a Rashba metal layer under a ferromagnetic exchange field. Within the quasiclassical Green's function framework, we derive analytical expressions for the first- and second-harmonic spin Josephson currents. The interplay between Rashba spin-orbit interaction and the exchange field breaks inversion and time-reversal symmetries, generating additional cosine terms in the spin current-phase relations and a finite phi0 phase shift. This phase shift induces an intrinsic asymmetry between forward and backward spin currents, leading to the SJDE without an external magnetic field. Numerical results show that the efficiency decreases with increasing metal thickness due to suppression of the second-harmonic component, while its dependence on spin-orbit interaction strength reflects competing effects between phase shift enhancement and harmonic suppression. These findings demonstrate that the interplay between harmonic components provides a mechanism for nonreciprocal spin transport without requiring suppression of spin-singlet correlations.
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