Domain walls in a tetragonal chiral p-wave superconductors with broken time reversal symmetry are analyzed in the framework of the Ginsburg-Landau theory. The energy and the jump of the magnetic induction on the wall were determined for different types of walls as functions of the parameters of the Ginzburg-Landau theory and orientation of the domain wall with respect to the crystallographic axes. We discuss implications of the analysis for $Sr_{2}RuO_{4}$, where no stray magnetic fields from domain walls were detected experimentally.
The transformation of the vortex lattice in a tetragonal superconductor which consists of its 45 degree reorientation relative to the crystal axes is studied using the nonlocal London model. It is shown that the reorientation occurs as two successive second order (continuous) phase transitions. The transition magnetic fields are calculated for a range of parameters relevant for borocarbide superconductors in which the reorientation has been observed.
The full-potential linearized augmented plane wave method with the generalized gradient approximation for the exchange and correlation potential (LAPW-GGA) is used to understand the electronic band structure of fluorine-arsenide SrFeAsF as a possible parent material for a new group of oxygen-free FeAs superconductors. The electronic bands, density of states, Fermi surface and atomic charges have been evaluated and discussed for high-temperature tetragonal and low-temperature orthorhombic SrFeAsF phases.
Effect of tetragonal distortion on the electronic structure, dynamical properties and superconductivity in Mo$_3$Sb$_7$ is analyzed using first principles electronic structure and phonon calculations. Rigid muffin tin approximation (RMTA) and McMillan formulas are used to calculate the electron-phonon coupling constant $λ$ and superconducting critical temperature. Our results show, that tetragonal distortion has small, but beneficial effect on superconductivity, slightly increasing $λ$, and the conclusion that the electron-phonon mechanism is responsible for the superconductivity in Mo$_3$Sb$_…
In superconductors with strong coupling between superconductivity and elasticity manifested in a strong dependence of transition temperature on pressure, there is an additional contribution to inter-vortex interactions due to the strain field generated by vortices. When vortex lines are along the $c$ axis of a tetragonal crystal, a square vortex lattice (VL) is favored at low vortex densities, because the vortex-induced strains contribution to the inter-vortex interactions is long range. At intermediate magnetic fields, the triangular lattice is stabilized. The triangular lattice evolves to th…
First principles FLAPW-GGA method was used for the comparative study of the structural and electronic properties of three related tetragonal ThCr2Si2-type phases KFe2Ch2, where Ch are S, Se, and Te. The main trends in electronic bands, densities of states and Fermi surfaces for AFe2Ch2 are analyzed in relation to their structural parameters. We found that at the anion replacements (S<->Se<->Te) any critical changes in electronic structure of KFe2Ch2 phases are absent. On the other hand, our analysis of structural and electronic parameters for hypothetical KFe2Te2 allows to assume that this sys…
We report the temperature dependent x-ray powder diffraction of the FeAs-based superconductors in the range between 300 K and 95 K. In the case of NdOFeAs we have detected the structural phase transition from the tetragonal phase, with P4/nmm space group, to the orthorhombic phase,with Cmma space group, over a broad temperature range from 150 K to 120 K, centered at T0 137K. This transition is reduced, by about 30K, by the internal chemical pressure going from LaOFeAs to NdOFeAs. On the contrary the superconducting critical temperature increases from 27K to 51 K going from LaOFeAs to NdOFeAs d…
We compute the topological phase diagram of 2D tetragonal superconductors for the only possible nodeless pairing channels compatible with that crystal symmetry. Subject to a Zeeman field and spin-orbit coupling, we demonstrate that these superconductors show surprising topological features: non-trivial high Chern numbers, massive edge states, and zero-energy modes out of high symmetry points, even though the edge states remain topologically protected. Interestingly, one of these pairing symmetries, $d+id$, has been proposed to describe materials such as water-intercalated sodium cobaltates, bi…
The hole doped Fe-based superconductors Ba$_{1-x}$A$_x$Fe$_2$As$_2$ (where A=Na or K) show a particular rich phase diagram. It was observed that an intermediate re-entrant tetragonal phase forms within the orthorhombic antiferromagnetically-ordered stripe-type spin density wave state above the superconducting transition [S. Avci et al., Nature Comm. 5, 3845 (2014), A. E. Böhmer et al., arXiv:1412.7038v2]. A similar intermediate phase was reported to appear if pressure is applied to underdoped Ba$_{1-x}$K$_x$Fe$_2$As$_2$ [E. Hassinger et al., Phys. Rev. B 86, 140502(R) (2012)]. Here we report d…
We have investigated the in-plane anisotropy of the c-axis magnetoresistance for single crystals of a BiCh2-based superconductor LaO0.5F0.5BiSSe under in-plane magnetic fields. We observed two-fold symmetry in the c-axis magnetoresistance in the ab-plane of LaO0.5F0.5BiSSe while the crystal possessed a tetragonal square plane with four-fold symmetry. The observed symmetry lowering in magnetoresistance from the structural symmetry may be related to the nematic states, which have been observed in the superconducting states of several unconventional superconductors.
We have examined theoretically the electronic band structure and Fermi surface of tetragonal low-temperature superconductor Bi2Pd. Our main results are that (i) the Pd 4d and Bi 6p states determine the main peculiarities of the multiple-sheets FS topology, thus for this material the complicated superconducting gap structure with different energy gaps on different FS sheets should be assumed; (ii) the effect of the spin-orbit coupling is of minor importance for the distributions of the near-Fermi electronic states; and (iii) this phase adopts 3D-like type owing to the directional bonds between …
Tetragonal FeSe is a superconductor with a transition temperature Tc of 8 K and shows a huge enhancement of Tc with applying pressure. Tetragonal FeTe has a structure very analogous to superconducting FeSe, but does not show superconducting transition. We investigated the pressure effect of resistivity on FeTe. The resistivity at room temperature decreased with increasing pressure. An anomaly in resistivity around 80 K shifted towards a lower temperature with increasing pressure.
A polycrystalline sample of FeSe, which adopts the tetragonal PbO-type structure (P4/nmm) at room temperature, has been prepared using solid state reaction. We have investigated pressure-induced structural changes in tetragonal FeSe at varying hydrostatic pressures up to 0.6 GPa in the orthorhombic (T = 50 K) and tetragonal (T = 190 K) phases using high resolution neutron powder diffraction. We report that the structure is quite compressible with a Bulk modulus around 31 GPa to 33 GPa and that the pressure response is anisotropic with a larger compressibility along the c-axis. Key bond angles …
We report temperature-dependent pair distribution function measurements of Sr$_{1-x}$Na$_{x}$Fe$_2$As$_2$, an iron-based superconductor system that contains a magnetic phase with reentrant tetragonal symmetry, known as the magnetic $C_4$ phase. Quantitative refinements indicate that the instantaneous local structure in the $C_4$ phase is comprised of fluctuating orthorhombic regions with a length scale of $\sim$2 nm, despite the tetragonal symmetry of the average static structure. Additionally, local orthorhombic fluctuations exist on a similar length scale at temperatures well into the parama…
Cubic Pm-3n Nb3Sn0.92 superconductor (Tc ~ 16 K) was found to exhibit tetragonal instabilities at the superconducting state (T = 10 K). These instabilities are manifested through the appearance of reflections which are forbidden in the Pm-3n symmetry but are compatible with the P42/mmc structure which is observed in the Nb3Sn1-x system for higher Sn content at temperatures lower than ~ 43 K. Nevertheless, the low-temperature structure of Nb3Sn0.92 remains metrically fully cubic, as concluded from single crystal synchrotron radiation diffraction experiments. Subsequent application of external p…
Very recently, the tetragonal BiOCuS was synthesized and declared as a new superconducting system with Fe-oxypnictide - related structure. Here, based on first-principle FLAPW-GGA calculations, the structural parameters, electronic bands picture, density of states and electron density distribution for BiOCuS are investigated for the first time. Our results show that, as distinct from related metallic-like FeAs systems, BiOCuS phase behaves as an ionic semiconductor with the calculated indirect band gap at about 0.48 eV. The superconductivity for BiOCuS may be achieved exclusively by doping of …
A15 Nb$_3$Si is, until now, the only high temperature superconductor produced at high pressure (~110 GPa) that has been successfully brought back to room pressure conditions in a metastable condition. Based on the current great interest in trying to create metastable-at-room-pressure high temperature superconductors produced at high pressure, we have restudied explosively compressed A15 Nb$_3$Si and its production from tetragonal Nb$_3$Si. First, diamond anvil cell pressure measurements up to 88 GPa were performed on explosively compressed A15 Nb$_3$Si material to trace Tc as a function of pre…
By performing pressure simulations within density functional theory for the family of iron-based superconductors $Ae{}A$Fe$_4$As$_4$ with $Ae$ = Ca, Sr, Ba and $A$ = K, Rb, Cs we predict in these systems the appearance of two consecutive half-collapsed tetragonal transitions at pressures $P_{c_1}$ and $P_{c_2}$, which have a different character in terms of their effect on the electronic structure. We find that, similarly to previous studies for CaKFe$_4$As$_4$, spin-vortex magnetic fluctuations on the Fe sublattice play a key role for an accurate structure prediction in these materials at zero…
In the temperature-concentration phase diagram of most iron-based superconductors, antiferromagnetic order is gradually suppressed to zero at a critical point, and a dome of superconductivity forms around that point. The nature of the magnetic phase and its fluctuations is of fundamental importance for elucidating the pairing mechanism. In Ba{1-x}KxFe2As2 and Ba{1-x}NaxFe2As2, it has recently become clear that the usual stripe-like magnetic phase, of orthorhombic symmetry, gives way to a second magnetic phase, of tetragonal symmetry, near the critical point, between x = 0.24 and x = 0.28. Here…
Recent experiments have reported that inserting metal atoms or small molecules in between the FeSe layers of $β$-FeSe can significantly enhance the superconducting transition temperature. Here, based on first-principles electronic structure calculations, we propose a stable compound SnOFeSe by alternatively stacking the SnO and $β$-FeSe layers. The predicted SnOFeSe has the same tetragonal structure as the well-known FeAs-based compound LaOFeAs, meanwhile their electronic structures in the nonmagnetic state are quite similar. The magnetic ground state of SnOFeSe is predicted to be the dimer an…
We claim that the charge density wave recently found by resonant soft x-ray scattering in layered copper oxides is the tetragonal symmetry defined by the distance between neighbor Cu$^{3+}$ ions in the CuO$_2$ layer that determines the critical temperature. We find evidence that this tetragonal symmetry is a skyrmionic state, which is responsible for an unusual magnetic order and charge flow in the layers that leads to the breaking of the time reversal symmetry below the pseudogap line. The core of the skyrmions form pockets of local magnetic field piercing the superconducting layers in opposi…
Here we establish a combined electronic phase diagram of isoelectronic FeSe1-xSx (0.19 > x > 0.0) and FeSe1-yTey (0.04 < y < 1.0) single crystals. The FeSe1-yTey crystals with y = 0.04 - 0.30 are grown by a hydrothermal ion-deintercalation (HID) method. Based on combined experiments of the specific heat, electrical transport, and angle-resolved photoemission spectroscopy, no signature of the tetragonal-symmetry-broken transition to orthorhombic (nematic) phase is observed in the HID FeSe1-yTey samples, as compared with the FeSe1-xSx samples showing this transition at Ts. A ubiquitous dip-like …
Iron-based superconductors are well-known for their intriguing phase diagrams, which manifest a complex interplay of electronic, magnetic and structural degrees of freedom. Among the phase transitions observed are superconducting, magnetic, and several types of structural transitions, including a tetragonal-to-orthorhombic and a collapsed-tetragonal transition. In particular, the widely-observed tetragonal-to-orthorhombic transition is believed to be a result of an electronic order that is coupled to the crystalline lattice and is, thus, referred to as nematic transition. Nematicity is therefo…
A huge enhancement of the superconducting transition temperature Tc was observed in tetragonal FeSe superconductor under high pressure. The onset temperature became as high as 27 K at 1.48 GPa and the pressure coefficient showed a huge value of 9.1 K/GPa. The upper critical field Hc2 was estimated to be ~ 72 T at 1.48 GPa. Because of the high Hc2, FeSe system may be a candidate for application as superconducting wire rods. Moreover, the investigation of superconductivity on simple structured FeSe may provide important clues to the mechanism of superconductivity in iron-based superconductors.
By means of first-principles calculations, the electronic structure and chemical bonding for the recently discovered tetragonal (s.g. P4/n; # 85) superconducting (Tc ~ 25K) phase Ca10(Pt4As8)(Fe2As2)5 have been examined in details, and the optimized structural parameters, electronic bands, densities of states, and inter-atomic bonding picture were evaluated and analyzed in comparison with related layered iron-based superconducting materials. We have shown that (i) Ca10(Pt4As8)(Fe2As2)5 is metallic-like, and the electronic bands in the window around the Fermi level are formed mainly by the Fe 3…
We calculate microscopically the interaction energy of domain walls separating degenerate ground states in a chiral p-wave superconductor. The interaction is mediated by the quasiparticles experiencing Andreev scattering at the domain walls. As a by-product, we derive a useful general expression for the free energy of an arbitrary nonuniform texture of the order parameter in terms of the quasiparticle scattering matrix.
We calculate microscopically the viscous friction coefficient and the effective mass of domain walls separating regions of opposite chirality in p-wave superconductors with k_x\pm ik_y order parameter. The domain wall viscosity and inertia are determined by the transitions between different Bogoliubov quasiparticle states induced by the domain wall motion. As a by-product, we present a detailed analysis of the quasiparticle spectrum, both bound and scattering, in the presence of a general domain wall with an arbitrary phase difference between the domains.
Domain walls can be formed in superconductors with a discrete degeneracy of the ground state, for instance, due to the breaking of time reversal symmetry. We study all cases where the formation of domain walls is possible in a tetragonal superconductor with the point group $D_{4h}$. We discuss both triplet and mixed singlet order parameters. It is found that in all cases the domain walls support subgap Andreev bound states, whose energies strongly depend on the direction of semiclassical propagation. The bound state contribution to the density of quasiparticle states exhibits peculiar features…
Nonequilibrium properties of short-coherence-length s-wave superconductors are analyzed in the presence of extrinsic and intrinsic inhomogeneities. In general, the lowest-energy configurations of quasiparticle excitations are topological textures where quasiparticles segregate into antiphase domain walls between superconducting regions whose order-parameter phases differ by $π$. Antiphase domain walls can be probed by various experimental techniques, for example, by optical absorption and NMR. At zero temperature, quasiparticles seldom appear as self-trapped bag states. However, for low concen…
We show that time reversal symmetry breaking $p_x+ip_y$ wave superconductors undergo several phase transitions subjected to external magnetic field or supercurrent. In such system the discrete $Z_2$ symmetry can recover before the complete destruction of the order parameter. The topological defects associated with $Z_2$ symmetry - domain walls can be created in a controllable way by magnetic field or current sweep according to the Kibble-Zurek scenario. Such domain wall generation can take place in exotic superconductors like $Sr_2RuO_4$ and some heavy fermion compounds.
Combined neutron and x-ray diffraction experiments demonstrate the formation of a low-temperature minority tetragonal phase in Ba$_{0.76}$K$_{0.24}$Fe$_2$As$_2$ in addition to the majority magnetic, orthorhombic phase. A coincident enhancement in the magnetic ($\frac{1}{2}$ $\frac{1}{2}$ 1) peaks shows that this minority phase is of the same type that was observed in Ba$_{1-x}$Na$_x$Fe$_2$As$_2$ ($0.24 \leq x \leq 0.28$), in which the magnetic moments reorient along the $c$-axis. This is evidence that the tetragonal magnetic phase is a universal feature of the hole-doped iron-based superconduc…
Chiral superconductors are two-fold degenerate and domains of opposite chirality can form, separated by domain walls. There are indications of such domain formation in the quasi two-dimensional putative chiral $p$-wave superconductor Sr$_2$RuO$_4$, yet no experiment has explicitly resolved individual domains in this material. In this work, $c$-axis domain walls lying parallel to the layers in chiral $p$-wave superconductors are explored from a theoretical point of view. First, using both a phenomenological Ginzburg-Landau and a quasiclassical Bogoliubov-deGennes approach, a consistent qualitat…
We review neutron scattering investigations of the crystal structures, magnetic structures, and spin dynamics of the iron-based RFe(As,P)O (R=La, Ce, Pr, Nd), (Ba,Sr,Ca)Fe2As2, and Fe1+x(Te-Se) systems. On cooling from room temperature all the undoped materials exhibit universal behavior, where a tetragonal-to-orthorhombic/monoclinic structural transition occurs, below which the systems become antiferromagnets. For the first two classes of materials the magnetic structure within the a-b plane consists of chains of parallel Fe spins that are coupled antiferromagnetically in the orthogonal direc…
We calculate the energy spectrum of quasiparticles trapped by a domain wall separating different time reversal symmetry-breaking ground states in a hexagonal superconductor, such as UPt$_3$. The bound state energy is found to be strongly dependent on the gap symmetry, the domain wall orientation, the quasiparticle's direction of semiclassical propagation, and the phase difference between the domains. We calculate the corresponding density of states and show how one can use its prominent features, in particular, the zero-energy singularity, to distinguish between different pairing symmetries.
We consider a system where structural polymorphism suggests the possible existence of superconductivity through the implied structural instability. SrPd2Bi2 has two poly-morphs which can be controlled by the synthesis temperature: a tetragonal form (CaBe2Ge2-type) and a monoclinic form (BaAu2Sb2-type). Though the crystallographic difference between the two forms may at first seem trivial, we show that tetragonal SrPd2Bi2 is superconducting at 2.0 K whereas monoclinic SrPd2Bi2 is not. We rationalize this finding and place it in context with other 1-2-2 phases
Arguments were recently advanced that hole-doped Ba$_{1-x}$K$_x$Fe$_2$As$_2$ exhibits $s+is$ state at certain doping. Spontaneous breaking of time reversal symmetry in $s+is$ state, dictates that it possess domain wall excitations. Here, we discuss what are the experimentally detectable signatures of domain walls in $s+is$ state. We find that in this state the domain walls can have dipole-like magnetic signature (in contrast to the uniform magnetic signature of domain walls $p+ip$ superconductors). We propose experiments where quench-induced domain walls can be stabilized by geometric barriers…
We perform a fully self-consistent study of domain walls between different chiral domains in chiral $d_{x^2-y^2} \pm id_{xy}-wave superconductors with an underlying honeycomb lattice structure. We investigate domain walls along all possible armchair and zigzag directions and with a finite global phase shift across the domain wall, in addition to the change of chirality. For armchair domain walls we find the lowest domain wall energy at zero global phase shift, while the most favorable zigzag domain wall has a finite global phase shift dependent on the doping level. Below the van Hove singulari…
Using angle resolved photoemission it is shown that the low lying electronic states of the iron pnictide parent compound EuFe$_2$As$_2$ are strongly modified in the magnetically ordered, low temperature, orthorhombic state compared to the tetragonal, paramagnetic case above the spin density wave transition temperature. Back-folded bands, reflected in the orthorhombic/ anti-ferromagnetic Brillouin zone boundary hybridize strongly with the non-folded states, leading to the opening of energy gaps. As a direct consequence, the large Fermi surfaces of the tetragonal phase fragment, the low temperat…
On the basis of phenomenological Ginzburg-Landau approach we investigate the problem of order parameter nucleation in hybrid superconductor/ferromagnetic systems with a domain structure in applied external magnetic field. Both the isolated domain boundaries and periodic domain structures in ferromagnetic layers are considered. We study the interplay between the superconductivity localized at the domain walls and far from the walls and show that such interplay determines a peculiar field dependence of the critical temperature Tc. For a periodic domain structure the behavior of the upper critica…
As the simplest iron-based superconductor, FeSe forms a tetragonal structure with transition temperature Tc ~ 8 K. With assistance of pressure, or other techniques, Tc can be greatly enhanced, even to above liquid nitrogen temperature. The newly discovered superconducting tetragonal FeS (Tc ~ 4.5 K), a sulfide counterpart of FeSe, promotes us on its high pressure investigation. The transport and structure evolution of FeS with pressure have been studied. A rapid suppression of Tc and vanishing of superconductivity at 4.0 GPa are observed, followed by a second superconducting dome with a 30% en…
We investigate the re-entrant tetragonal phase in the iron-based superconductor Ba0 .76K0.24Fe2As2 by DC magnetization and thermoelectrical measurements. The reversible magnetization confirms by a thermodynamic method that the spin alignment in the re-entrant C4 phase is out-of-plane, in agreement with an itinerant double-Q magnetic order [Allred et al., Nat. Phys. 12, 493 (2016)]. The Nernst coefficient shows the typical unusually large negative value in the stripe-type spin density wave (SDW) state owing to the Fermi surface reconstruction associated with SDW and nematic order. At the transi…
Twin boundaries in orthorhombic d-wave superconductors are investigated numerically using the Bogoliubov-deGennes formalism within the context of an extended Hubbard model. The twin boundaries are represented by tetragonal regions of variable width, with a reduced chemical potential. For sufficiently large twin boundary width and change in chemical potential, an induced s-wave component may break time-reversal symmetry at a low temperature. This temperature, and the magnitude of the complex component, are found to depend strongly on electron density. The results are compared with recent tunnel…
We consider the effect of magnetic impurities, modeled by classical spins, in a conventional superconductor. We study their effect on the quasiparticles, specifically on the spin density and local density of states (LDOS). As previously emphasized, the impurities induce multiple scatterings of the quasiparticle wave functions leading to complex interference phenomena. Also, the impurities induce quantum phase transitions in the many-body system. Previous authors studied the effect of either a small number of impurities (from one to three) or a finite concentration of impurities, typically in a…
We investigate how domain structure of the ferromagnet in superconductor-ferromagnet heterostructures may change their transport properties. We calculate the distribution of current in the superconductor induced by magnetic field of Bloch domain walls, find the ``lower critical'' magnetization of the ferromagnet that provides vortices in the superconductor.
The rhombic-to-square transition field $H_{\Box}(T)$ for cubic and tetragonal materials in fields along [001] is evaluated using the nonlocal London theory with account of thermal vortex fluctuations. Unlike extended Ginzburg-Landau models, our approach shows that the line $H_{\Box}(T)$ and the upper critical field $H_{c2}(T)$ do not cross due to strong fluctuations near $H_{c2}(T)$ which suppress the square anisotropy induced by the nonlocality. In increasing fields, this causes re-entrance of the rhombic structure in agreement with recent neutron scattering data on borocarbides.
We study dynamics of a superconducting condensate in the presence of a domain wall defect in the order parameter. We find that broken translation and reflection symmetries result in new collective excitations, bound to the domain wall region. Two additional amplitude/Higgs modes lie below the bulk pairbreaking edge $2Δ$; one of them is a Goldstone mode with vanishing excitation energy. Spectrum of bound collective modes is related to the topological structure and stability of the domain wall. The `unbound' bulk collective modes and transverse gauge field mostly propagate across the domain wall…
The interaction between a magnetic thin film and a superconductor is studied. In particular, the equilibrium width of a Bloch wall is estimated with and without the superconductor. It is shown that the Bloch wall experiences a small shrinkage on cooling through the critical temperature of the superconductor. Furthermore, the interaction between the Bloch wall and a single vortex is estimated, and a simple expression for the force is found.
It is conjectured that the anomalous spin dynamics observed in the normal state of cuprate superconductors might find its origin in a nearly ordered spin system which is kept in motion by thermally meandering charged domain walls. `Temperature sets the scale' finds a natural explanation, while a crossover to a low temperature quantum domain wall fluid is implied.
The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state of a two-dimensional (2D) orthorhombic lattice superconductor is studied based on the Bogoliubov-de-Gennes equations. It is illustrated that the 2D FFLO state is suppressed and only one-dimensional (1D) stripe state is stable. The stripe changes its orientation with the increasing Zeeman field. There exists a crossover region where the gap structure has some local 2D features. These results are significantly different from those of the tetragonal lattice system. The local density of states is also studied which can be checked and compared with …
We present a systematic study of the magnetic domain wall induced modulation of superconducting transition temperature (Tc) in Nb/Ni bilayer stripes. By varying the thickness of the Ni layer from 20 nm to 100 nm we have been able to measure the low field Tc-H phase diagram spanning the Neel domain wall and Bloch domain wall range of thicknesses. Micromagnetic simulations and magnetic force microscopy measurements confirmed a stronger out-of-plane stray field in the Bloch domain walls compared to the Neel walls. A suppression in Tc was observed in the magnetization reversal region of the Ni fil…
Contrary to the usual assumption, the electron Bloch states in crystals with spin-orbit coupling do not always transform under symmetry operations in the same way as the pure spin-1/2 states. This has profound consequences for the symmetry properties and nodal structure of superconductors, especially for the interband gap functions. Focusing on tetragonal superconductors, we show that the interband pairing in the conventional (s-wave) channel can have features which are traditionally associated with unconventional pairing, such as triplet components and odd parity, and can produce line nodes i…
We theoretically investigate domain wall motion in an antiferromagnetic insulator layer caused by thermally generated spin currents in an adjacent spin-split superconductor layer. An uncompensated antiferromagnet interface enables the two crucial ingredients underlying the mechanism - spin splitting in the superconductor and absorption of spin currents by the antiferromagnet. Treating the superconductor using the quasiclassical theory and the antiferromagnet via Landau-Lifshitz-Gilbert description, we find domain wall propagation along the thermal gradient with relatively large velocities $\si…
One of the defining features of spontaneously broken time-reversal symmetry (BTRS) is the existence of domain walls, the detection of which would be strong evidence for such systems. There is keen interest in BTRS currently, in part, due to recent muon spin rotation experiments, which have pointed towards $\textrm{Ba}_{1-x}\textrm{K}_x\textrm{Fe}_2\textrm{As}_2$ exhibiting a remarkable case of $s$-wave superconductivity with spontaneously broken time-reversal symmetry. A key question, however, is how to differentiate between the different theoretical models which describe such a state. Two par…
A ferromagnetic insulator (FI) in contact with a superconductor (S) is known to induce a spin splitting of the BCS density of states at the FI/S interface. This spin splitting causes the Cooper pairs to reduce their singlet-state correlations and acquire odd-in-frequency triplet correlations. We consider a diffusive FI/S bilayer with a sharp magnetic domain wall in the FI and study the local quasiparticle density of states and triplet superconducting correlations. In the case of collinear alignment of the domains, we obtain analytical results by solving the Usadel equation. For a small enough …
Relaxation Dynamics of Superconducting/Normal Interfaces in the Intermediate State of a type-I superconductor
Low Temperature Physics Laboratory, College of Physics & Center of Quantum Materials and Devices, Chongqing University（重庆大学物理学院低温物理实验室与量子材料与器件中心）；Materials Genome Institute, Shanghai University（上海大学材料基因组研究院）
A simulation study for the magnetization process is performed for the multi-domain state in a chiral p-wave superconductor, using the time-dependent Ginzburg-Landau theory. The external field penetrates inside as core-less vortices through the domain wall, forming the vortex sheet structure. We find that, with increasing magnetic fields, the domain walls move so that the unstable domains shrink to vanish. Therefore, the single domain structure is realized at higher fields.
