Using numerical renormalization group we study thermodynamic properties of a magnetic impurity described by the Anderson impurity model in a superconducting host material described by the BCS Hamiltonian. When the Kondo temperature in the normal state, T_K, is comparable to the critical temperature of the superconducting transition, T_c, the magnetic doublet state may become degenerate with the Kondo singlet state, leading to a ln3 peak in the temperature dependence of the impurity contribution to the entropy. This entropy increase translates into an anomalous feature in the heat capacity which might have already been experimentally observed.
We study the Kondo physics of a quantum magnetic impurity in two-dimensional topological superconductors (TSCs), either intrinsic or induced on the surface of a bulk topological insulator, using a numerical renormalization group technique. We show that, despite sharing the p + ip pairing symmetry, intrinsic and extrinsic TSCs host different physical processes that produce distinct Kondo signatures. Extrinsic TSCs harbor an unusual screening mechanism involving both electron and orbital degrees of freedom that produces rich and prominent Kondo phenomena, especially an intriguing pseudospin Kond…
Junction systems of odd-frequency (OF) superconductors are investigated based on a mean-field Hamiltonian formalism. One-dimensional two-channel Kondo lattice (TCKL) is taken as a concrete example of OF superconductors. Properties of normal and Andreev reflections are examined in a normal metal/superconductor junction. Unlike conventional superconductors, normal reflection is always present due to the normal self energy that necessarily appears in the present OF pairing state. The conductance reflects the difference between repulsive and attractive potentials located at the interface, which is…
The hybridization of magnetism and superconductivity has been an intriguing playground for correlated electron systems, hosting various novel physical phenomena. Usually, localized d- or f-electrons are central to magnetism. In this study, by placing a PTCDA (3,4,9,10-perylene tetracarboxylic dianhydride) molecular monolayer on ultra-thin Pb films, we built a hybrid magnetism/superconductivity (M/SC) system consisting of only sp electronic levels. The magnetic moments reside in the unpaired molecular orbital originating from interfacial charge-transfers. We reported distinctive tunneling spect…
We give a brief review of the Mott-Kondo scenario and its consequence in the recently-discovered infinite-layer nickelate superconductors. We argue that the parent state is a self-doped Mott insulator and propose an effective $t$-$J$-$K$ model to account for its low-energy properties. At small doping, the model describes a low carrier density Kondo system with incoherent Kondo scattering at finite temperatures, in good agreement with experimental observation of the logarithmic temperature dependence of electric resistivity. Upon increasing Sr doping, the model predicts a breakdown of the Kondo…
Using the numerical renormalization group method, the effect due to a Kondo impurity in an $s$-wave superconductor is examined at finite temperature ($T$). The $T$-behaviors of the spectral function and the magnetic moment at the impurity site are calculated. At $T$=0, the spin due to the impurity is in singlet state when the ratio between the Kondo temperature $T_k$ and the superconducting gap $Δ$ is larger than 0.26. Otherwise, the spin of the impurity is in a doublet state. We show that the separation of the double Yu-Shiba-Rusinov peaks in the spectral function shrinks as $T$ increases if …
The competition of the free spin state of a paramagnetic impurity on a superconductor with its screened counterpart is characterized by the energy scale of Kondo screening $k_BT_K$ compared to the superconducting pairing energy $Δ$. When the experimental temperature suppresses Kondo screening, but preserves superconductivity, i.e., when $Δ/k_B > T > T_K$, this description fails. Here, we explore this temperature range in a set of manganese phthalocyanine molecules decorated with ammonia (MnPc-NH$_3$) on Pb(111). We show that these molecules suffice the required energy conditions by exhibiting …
Using the framework of the density-matrix renormalization group (DMRG), we study a quantum dot coupled to a superconducting nanowire with strong Rashba spin-orbit coupling. Regarding the singlet-to-doublet "0-$π$" transition that takes place when the Kondo effect is overcome by the superconducting gap, we show that the Rashba coupling modifies the critical values at which the transition occurs, favouring the doublet phase. In addition, using a generalized Haldane's formula for the Kondo temperature $T_K$, we show that it is lowered by the Rashba coupling. We benchmark our DMRG results comparin…
Spin splitting, Kondo correlation and singlet-doublet quantum phase transition in a superconductor-coupled InSb nanosheet quantum dot
Beijing Academy of Quantum Information Sciences（北京量子信息科学研究院）；Hangzhou International Innovation Institute, Beihang University（北京航空航天大学杭州创新研究院）；Peking University（北京大学）
Using Ginzburg-Landau formalism, we theoretically study the isothermal shear modulus anomaly of an unconventional superconductor with a multicomponent order parameter, when the superconducting transition is split by a symmetry-breaking field. Experimental signatures are proposed for both chiral and nematic superconductors. Particularly striking is the vanishing of $C_{66}$ across the lower transition to a nematic superconducting state. Our findings can guide future experiments and shed new lights on materials such as Sr$_2$RuO$_4$ and $M_x$Bi$_2$Se$_3$.
We propose that chiral anomaly of Weyl superconductors gives rise to negative thermal magnetoresistivity induced by emergent magnetic fields, which are generated by vortex textures of order parameters or lattice strain. We establish this scenario by combining the argument based on Berry curvatures, and the quasi-classical theory of the Eilenberger equation with quantum corrections arising from inhomogeneous structures. It is found that the chiral anomaly contribution of the thermal conductivity exhibits characteristic temperature dependence, which can be a smoking-gun signature of this effect.
Unconventional superconductivity from heavy fermion (HF) is always observed in f-electron systems, in which Kondo physics between localized f-electrons and itinerant electrons plays an essential role. Whether HF superconductivity could be achieved in other systems without f electrons, especially for d-electron systems, is still elusive. Here, we experimentally study the origin of d-electron HF behavior in iron-based superconductors (FeSCs) AFe2As2 (A = K, Rb, Cs). Nuclear magnetic resonance on 75As reveals a universal coherent-incoherent crossover with a characteristic temperature T*. Below T*…
We report on transport features in heavily boron doped nanocrystalline diamond (BNCD) films which are not seen in conventional (s-wave) granular superconductors. Observations include an anomalous resistance peak near to the superconducting transition temperature as well as a strong zero bias conductance peak in the current-voltage spectra. The effect of finite bias current on the evolution of the resistance peak is systematically investigated in this system. The shape of the resistance-temperature curves near the critical temperature is seen to be strongly influenced by both magnetic field and…
The heavy quasiparticle bands in Kondo materials which originate in the hybridization of f- and conduction electrons exhibit numerous, sometimes coexisting, broken symmetry phases. Most notable are unconventional superconductivity, itinerant small moment antiferromagnetism and hidden order of higher order multipoles of f-electrons which all lead to a gapping of the heavy bands. In rare cases the chemical potential lies within the hybridization gap and the ground state is a Kondo semiconductor without ordering. The dynamical magnetic response of such gapped f-electron systems has been investiga…
We study multiterminal Majorana and conventional superconducting islands in the vicinity of the charge degeneracy point using bosonization and numerical renormalization group. Both models map to the multichannel charge Kondo problem, but for noninteracting normal leads they flow to different non-Fermi liquid fixed points at low temperatures. We compare and contrast both cases by numerically obtaining the full crossover to the low temperature regime and predict distinctive transport signatures. We attribute the differences between both types of islands to a crucial distinction of charge-$2e$ an…
We study the properties of a quantum dot coupled to a one-dimensional topological superconductor and a normal lead and discuss the interplay between Kondo and Majorana-induced couplings in quantum dot. The latter appears due to the presence of Majorana zero-energy modes localized at the ends of the one-dimensional superconductor. We investigate the phase diagram of the system as a function of Kondo and Majorana interactions using a renormalization-group analysis, a slave-boson mean-field theory and numerical simulations using the density-matrix renormalization group method. We show that, in ad…
Realization of Kondo lattice in superconducting van der Waals materials not only provides a unique opportunity for tuning the Kondo lattice behavior by electrical gating or intercalation, but also is helpful for further understanding the heavy fermion superconductivity. Here we report a low-temperature and vector-magnetic-field scanning tunneling microscopy and spectroscopy study on a superconducting compound (4Hb-TaS2) with alternate stacking of 1T-TaS2 and 1H-TaS2 layers. We observe the quasi-two-dimensional superconductivity in the 1H-TaS2 layer with anisotropic response to the in-plane and…
Local Quasiparticle States near a Unitary Impurity with Induced Magnetic Moment in a d-Wave Superconductor
用从玻色子平均场方法研究了d波超导体中具有近藤类磁矩的幺正杂质的局域准粒子态密度.将哈密顿量严格对角化，得到了自洽的结果。我们发现，强杂质势散射和近藤效应之间的干扰导致新的准粒子光谱周围的杂质，这是显着不同的情况下，一个单一的单一或磁性杂质。最近在高T_c铜氧化物中Zn杂质周围的局域微分隧穿电导的STM图像可以从本质上解释，如果针尖和探测的CuO_2平面之间的BiO表面层的阻挡效应[Zhu et al.，Phys.Rev.B62，6207（2000）]。
An approach to bound states based on unitary transformations of Hamiltonians is presented. The method is applied to study the interaction between electrons in a BCS $s$-wave superconductor and a quantum spin. It is shown that known results from the t-matrix method and numerical studies are reproduced by this new method. As a main advantage, the method can straightforwardly be extended to study the topological properties of combined bound states in chains of many magnetic impurities. It also provides a uniform picture of the interplay between the Yu-Shiba-Rusinov (YSR) bound states and the Kond…
Evolution of the specific-heat anomaly of the high-temperature superconductor YBa2Cu3O7 under influence of doping through application of pressure up to 10 GPa
A one-dimensional time-reversal-invariant topological superconductor hosts a Majorana Kramers pair at each end, where time-reversal symmetry acts as a supersymmetry that flips local fermion parity. We examine the transport anomaly of such a superconductor, floating and tunnel-coupled to normal leads at its two ends. We demonstrate the realization of a topologically-protected, channel-symmetric, two-channel Kondo effect without fine-tuning. Whereas the nonlocal teleportation vanishes, a lead present at one end telecontrols the universal transport through the other end.
A new ternary platinum phosphide CePt$_{3}$P was synthesized and characterized by means of magnetic, thermodynamic and transport measurements. The compound crystallizes in an antiperovskite tetragonal structure similar to that in the canonical family of platinum-based superconductors $A$Pt$_{3}$P ($A$ = Sr, Ca, La) and closely related to the noncentrosymmetric heavy fermion superconductor CePt$_{3}$Si. In contrast to all the superconducting counterparts, however, no superconductivity is observed in CePt$_{3}$P down to 0.5 K. Instead, CePt$_{3}$P displays a coexistence of antiferromagnetic orde…
Competition between phonon superconductivity and Kondo screening in mixed valence and heavy fermion compounds
本文用周期Anderson模型的唯象方法研究了重费米子和混合价超导体中近藤效应与s波超导性的竞争。类似于超导体中单杂质近藤效应的已知结果，我们在较窄的模型参数和f电子浓度范围内，发现了重费米子超导体中超导转变温度$T_c$的重入区的主要可能性。混合价超导体中$T_c$的抑制作用要弱得多。在没有$T_c$重入行为的低温费米液相区，我们的理论是最有效的。为了检验其适用性，我们对Ce $_{1-x}$ La $_x$ Ru $_3$ Si $_2$中的$T_c$的$x$依赖性进行了拟合，并获得了与实验数据的极好的一致性，尽管在这种情况下没有发现再进入。根据我们的理论分析讨论了其他实验数据。特别是，我们比较了一些已知同系物的超导转变温度，即，具有和不具有f元素的模拟周期晶格化合物。对于少数几对同系物，超导电性只存在于重费米子材料中，从而证实了后者的超导电性机制的唯一性。我们认为，对于某些其他化合物的$T_c$的值可能保持在相同的数量级在两个同系物，如果超导性主要起源于一些轻费米表面，但诱导相当大的超导能隙在另一个费米表面，其中杂化或其他重费米子效应更显着。
