The electrical resistance of CeFeAsO$_{1-x}$F$_x$ (x = 0.06 and 0.08) has been measured in a magnetic field up to 40T. At zero field, the sample with x = 0.06 shows a structural phase transition around T$_S$~100K, followed by a spin-density-wave (SDW) transition around T$_{SDW}$~30K. For x = 0.08, the structural phase transition is suppressed down to T$_S$~60K without a clear anomaly associated with the Fe-SDW transition, and superconductivity shows up at T$_C$~25K. At lower temperatures, both samples show a clear resistive peak around T$_N$~4K, which is associated with the antiferromagnetic (AFM) transition of Ce-4f electrons. Strikingly, zero resistance is recovered upon further lowering temperature below T$_N$ for x = 0.08. Moreover, we found that the AFM transition of Ce 4f-electrons at 4K hardly changes with applying a magnetic field up to 40T, even in the case of x = 0.08, where superconductivity has been partially suppressed at such a large field.
In the iron-pnictide material CeFeAsO not only the Fe moments, but also the local 4f moments of the Ce order antiferromagnetically at low temperatures. We elucidate on the peculiar role of the Ce on the emergence of superconductivity. While application of pressure suppresses the iron SDW ordering temperature monotonously up to 4 GPa, the Ce-4f magnetism is stabilized, until both types of magnetic orders disappear abruptly and a narrow SC dome develops. With further increasing pressure characteristics of a Kondo-lattice system become more and more apparent in the electrical resistivity. This su…
Superconductivity distorted by the coexisting pseudogap in the antinodal region of Bi$_{1.5}$Pb$_{0.55}$Sr$_{1.6}$La$_{0.4}$CuO$_{6+δ}$: A photon-energy-dependent angle-resolved photoemission study
超导电性和赝能隙之间的相互作用是铜氧化物物理的一个重要方面。然而，赝能隙的性质仍然存在争议，部分原因是不同的实验提出了不同的能隙函数。本文采用光子能量依赖角分辨光电子能谱（ARPES）研究了Bi $_{1.5}$ Pb $_{0.55}$ Sr $_{1.6}$ La $_{0.4}$ CuO $_{6+δ}$ .我们发现，在低光子能量的反节ARPES谱是由背景信号，这可能会导致一个错误的评估的光谱间隙的大小占主导地位。一旦背景是适当的占，独立的光子能量，在不同的能量下，主要归因于赝能隙和超导性，以及偏离一个简单的d-波形式的整体光谱间隙的波腹光谱鲁棒地显示两个共存的功能。这些结果支持了赝能隙和超导性之间的竞争导致能隙畸变的观点。
Nonmonotonic $d_{x^2-y^2}$ superconducting gap in electron-doped Pr$_{0.89}$LaCe$_{0.11}$CuO$_4$: Evidence of coexisting antiferromagnetism and superconductivity?
We discuss superconductivity in a model on a cubic lattice for a $Γ_3$ non-Kramers system. In previous studies, it is revealed that $d$-wave superconductivity with $E_g$ symmetry occurs in a wide parameter range in a $Γ_3$ system. Such anisotropic superconductivity can break the cubic symmetry of the lattice. In a $Γ_3$ system, the quadrupole degrees of freedom are active and the effect of the cubic symmetry breaking should be important. Here, we investigate the coexisting states of the $d$-wave superconductivity and quadrupole order by a mean-field theory. In particular, we discuss possible c…
Superconductivity coexisting with phase-separated static magnetic order in (Ba,K)Fe$_{2}$As$_{2}$, (Sr,Na)Fe$_{2}$As$_{2}$ and CaFe$_{2}$As$_{2}$
FeAs基超导体的最新发现和后续发展为相关电子系统中超导机制的探索提出了新的挑战和机遇。正在进行的研究的中心问题包括超导性和磁性之间的相互作用，以及超导能隙中反映的配对对称性的性质。在铜氧化物和RE（O，F）FeAs（RE =稀土）体系中，除了相界边界处的窄相分离区外，出现了超导相，而没有伴随静态磁序。通过对单晶样品的μ子自旋弛豫测量，我们证明了在AFe $_{2}$ As $_{2}$（A = Ca，Ba，Sr）系统中，在组分调谐和压力调谐的情况下，超导电性与部分体积分数的强静磁序共存。超流响应从剩余的顺磁体积分数的（Ba $_{0.5}$ K $_{0.5}$）Fe $_{2}$ As $_{2}$在低温下表现出一个接近线性的T变化，表明各向异性能隙与线节点和/或多间隙效应。
Anomalous Zeeman response in coexisting phase of superconductivity and spin-density wave as a probe of extended $s$-wave pairing structure in ferro-pnictide
Topological superconductivity in multiband systems has received much attention due to a variety of possible exotic superconducting order parameters as well as non-trivial bulk and surface states. While the impact of coexisting magnetic order on superconductivity has been studied for many years, such as ferromagnetic superconductors, the implication of coexisting multipolar order has not been explored much despite the possibility of multipolar hidden order in a number of $f$-electron materials. In this work, we investigate topological properties of multipolar superconductors that may arise when…
ZrSiS was recently shown to be a new material with topologically non-trivial band structure which exhibits multiple Dirac nodes and a robust linear band dispersion up to an unusually high energy of 2\,eV. Such a robust linear dispersion makes the topological properties of ZrSiS insensitive to perturbations like carrier doping or lattice distortion. Here we show that a novel superconducting phase with a remarkably high $T_c$ of 7.5\,K can be induced in single crystals of ZrSiS by a non-superconducting metallic tip of Ag. From first-principles calculations we show that the observed superconducti…
Low-dimensional materials with broken inversion symmetry and strong spin-orbit coupling can give rise to fascinating quantum phases and phase transitions. Here we report coexistence of superconductivity and ferromagnetism below 2.5\,K in the quasi-one dimensional crystals of non-centrosymmetric (TaSe$_4$)$_3$I (space group: $P\bar{4}2_1c$). The unique phase is a direct consequence of inversion symmetry breaking as the same material also stabilizes in a centro-symmetric structure (space group: $P4/mnc$) where it behaves like a non-magnetic insulator. The coexistence here upfront contradicts the…
Coexisting electronic smectic liquid crystal and superconductivity in a Si square-net semimetal
RIKEN Center for Emergent Matter Science（理化学研究所新兴物质科学中心）；Institute for Solid State Physics, The University of Tokyo（东京大学固体物理研究所）；Department of Physics and Center for Theoretical Physics, National Taiwan University（国立台湾大学物理系暨理论物理中心）；Department of Applied Physics, Nagoya University（名古屋大学应用物理系）；Institute of Multidisciplinary Research for Advanced Materials, Tohoku University（东北大学先进材料跨学科研究所）；Physics Division, National Center for Theoretical Sciences（国家理论科学中心物理分部）
The defining characteristic of hole-doped cuprates is $d$-wave high temperature superconductivity. However, intense theoretical interest is now focused on whether a pair density wave state (PDW) could coexist with cuprate superconductivity (D. F. Agterberg et al., Annual Review of Condensed Matter Physics 11, 231 (2020)). Here, we use a strong-coupling mean-field theory of cuprates, to model the atomic-scale electronic structure of an eight-unit-cell periodic, $d$-symmetry form factor, pair density wave (PDW) state coexisting with $d$-wave superconductivity (DSC). From this PDW+DSC model, the …
Competing unconventional superconductivity and antiferromagnetism widely exist in several strongly correlated quantum materials whose direct simulation generally suffers from fermion sign problem. Here we report unbiased Quantum Monte Carlo (QMC) simulations on a sign-problem-free repulsive toy model with same onsite symmetries as the standard Hubbard model on a 2D square lattice. Using QMC, supplemented with mean-field and continuum field-theory arguments, we find that it hosts three distinct phases: a nodal d-wave phase, an antiferromagnet, and an intervening phase which hosts coexisting ant…
Recent experiments have pointed to a chiral p-wave-like superconductivity in epitaxial Bi/Ni bilayers that are spontaneously time-reversal symmetry breaking (TRSB), making it a promising platform for exploring physics useful for topologically protected quantum computing. Quite intriguingly, evidence has emerged that in non-epitaxial Bi/Ni bilayers, superconductivity arises due to the formation of NiBi3, which has been reported to host coexisting ferromagnetic and superconducting orders at the surface. We perform high resolution surface magneto-optic Kerr effect (SMOKE) measurements using a Sag…
We study superconductivity in the Hubbard model on various quasi-one-dimensional lattices with coexisting wide and narrow bands originating from multiple sites within a unit cell, where each site corresponds to a single orbital. The systems studied are the 2-leg and 3-leg ladders, the diamond chain, and the criss-cross ladder. These one-dimensional lattices are weakly coupled to form two-dimensional (quasi-one-dimensional) ones, and the fluctuation exchange approximation is adopted to study spin-fluctuation-mediated superconductivity. When one of the bands is perfectly flat, and the Fermi leve…
In the correlated electron system with the pseudogap, there are full-gapped domains and Fermi-arced domains coexisting. Those domains are created by the quantum-fluctuated antiferromagnetic fluctuations that generate the short-ranged attractive potential to produce the Fermi arcs and the superconductivity. In the full-gapped domains, s-wave or (d_{x^2-y^2}\pm id_{xy})-wave symmetry of the electron pairs is favored. In the Fermi-arced domains, only d_{x^2-y^2}-wave symmetry of pairs is stable. Superconductivity of different pairing symmetry coexists in different domains, as well. Different from…
We present here, the effect of microstructure on the magnetic, electrical and thermal properties of (V$_{0.60}$Ti$_{0.40}$)-Gd alloys. The gadolinium is found to be immiscible and precipitates with a size $<$1.2~$μ$m in the (V$_{0.60}$Ti$_{0.40}$)-Gd alloys. These precipitates enhance the grain boundary density. The (V$_{0.60}$Ti$_{0.40}$)-Gd alloys become ferromagnetic below $T_{mc}$ = 295~K with an increase in the superconducting transition temperature ($T_{sc}$). Though the disorder increases with increasing Gd content, the electronic thermal conductivity ($κ_{e} (H = 0)$) reduces by at mos…
Multilayered cuprates possess not only the highest superconducting temperature transition but also offer a unique platform to study disorder-free CuO$_2$ planes and the interplay between competing orders with superconductivity. Here, we study the underdoped trilayer cuprate HgBa$_2$Ca$_2$Cu$_3$O$_{8+ δ}$ and we report the first quantum oscillation and Hall effect measurements in magnetic field up to 88 T. A careful analysis of the complex spectra of quantum oscillations strongly supports the coexistence of an antiferromagnetic order in the inner plane and a charge order in the outer planes. Th…
The nature of superconductivity in newly discovered Kagome materials, $\text{AV}_3\text{Sb}_5$ (A=K, Rb, Cs), has been a subject of intense debate. Recent experiments suggest the presence of orbital current order on top of the charge density wave (CDW) and superconductivity. Since the orbital current order breaks time-reversal symmetry, it may fundamentally affect possible superconducting states. In this work, we investigate the mutual influence between the orbital current order and superconductivity in Kagome metal with characteristic van Hove singularity (vHS). By explicitly deriving the Lan…
We report pressure evolution of charge density wave (CDW) order and emergence of superconductivity (SC) in 1T-VSe2 single crystal by studying resistance and magnetoresistance behavior under high pressure. With increasing quasi-hydrostatic pressure the CDW order enhances with increase ofthe ordering temperature up to 240K at 12 GPa. Upon further increase of pressure, the resistance anomaly due to CDW order gets suppressed drastically and superconductivity emerges at ~15 GPa, with the onset critical temperature (Tc) ~ 4K. The pressure dependence of Tc is found negligible, different from the sign…
