The quantum spin liquid candidate NaYbSe$_2$ was recently reported to exhibit a Mott transition under pressure. Superconductivity was observed in the high-pressure metallic phase, raising the question concerning its relation with the low-pressure quantum spin liquid ground state. Here we combine the density functional theory and the dynamical mean-field theory to explore the underlying mechanism of the insulator-to-metal transition and superconductivity and establish an overall picture of its electronic phases under pressure. Our results suggest that NaYbSe$_2$ is a charge-transfer insulator at ambient pressure. Upon increasing pressure, however, the system first enters a semi-metallic state with incoherent Kondo scattering against coexisting localized Yb-$4f$ moments, and then turns into a heavy fermion metal. In between, there may exist a delocalization quantum critical point responsible for the observed non-Fermi liquid region with linear-in-$T$ resistivity. The insulator-to-metal transition is therefore a two-stage process. Superconductivity emerges in the heavy fermion phase with well-nested Yb-4$f$ Fermi surfaces, suggesting that spin fluctuations may play a role in the Cooper pairing. NaYbSe$_2$ might therefore be the 3rd Yb-based heavy-fermion superconductor with a very "high" $T_c$ than most heavy fermion superconductors.
The Mott transition is one of the fundamental issues in condensed matter physics, especially in the system with antiferromagnetic long-range order. However the Mott transition in quantum spin liquid (QSL) systems without long-range order is rare. Here we report the observation of the pressure-induced insulator to metal transition followed by the emergence of superconductivity in the QSL candidate NaYbSe2 with triangular lattice of 4f Yb$_3^+$ ions. Detail analysis of transport properties at metallic state shows an evolution from non-Fermi liquid to Fermi liquid behavior when approaching the vi…
Beyond the conventional electron pairing mediated by phonons, high-temperature superconductivity in cuprates is believed to stem from quantum spin liquid (QSL). The unconventional superconductivity by doping a spin liquid/Mott insulator, is a long-sought goal but a principal challenge in condensed matter physics because of the lack of an ideal QSL platform. Here we report the pressure induced metallization and possible unconventional superconductivity in $NaYbSe_{2}$, which belongs to a large and ideal family of triangular lattice spin liquid we revealed recently and is evidenced to possess a …
$\tilde{S}\!=\!1/2$ triangular-lattice $f$-electron materials define a dynamic research area in condensed matter magnetism. In various Yb 4$f^{13}$ triangular-lattice compounds, for example, spin-liquid ground states seem to be realized. Using {\it ab initio} quantum chemical methods, we here investigate how correlation effects involving the 4$f$ electrons affect the on-site $f$-$f$ excitation spectrum in NaYbSe$_2$. The system is well suited for such a study since unambiguous inelastic neutron scattering data are available for the Yb$^{3+}$ $f$-$f$ transitions. The excitation energies obtaine…
A three-orbital model derived from the two-dimensional projection of the $ab$ $initio$ Hamiltonian for alkaline doped fullerene A$_3$C$_{60}$ with A=Cs,Rb,K is studied by a variational Monte Carlo method. We correctly reproduce the experimental isotropic s-wave superconductivity around the $ab$ $initio$ parameters. With narrowing the bandwidth, the transition to an insulator is also reproduced, where orbital symmetry is found to be spontaneously broken with emergence of an excitonic Mott insulator for two orbitals and an antiferromagnetic insulator nearly degenerate with a spin liquid for the …
Superconductor-insulator transition is a fascinating quantum phenomenon that reveals a competition between phase order and charge localization. Microwave spectroscopy provides a novel promising approach to its controllable investigation in 1D Josephson arrays.
Motivated by superconductivity (SC) in layered nitrides, we study an ionic-Hubbard model on a honeycomb lattice, which consists of two sublattices with an energy-level offset, by using an optimization variational Monte Carlo method. Parameter values for the Coulomb interaction and the energy-level offset, to realize a band insulator in non-doped state, are evaluated, and the SC state is investigated in a carrier-doped band insulator. It is found that, in a weakly doped band insulator, spin fluctuation remains and the spin-singlet d-wave SC state is realized. Present results support an unconven…
Starting from the d-wave RVB mean-field theory of Kotliar and Liu, we present a new, long-wavelength/low-energy exact, treatment of gauge fluctuations. The result is a theory of gapless fermion quasiparticles coupled to superconducting phase fluctuations. We will discuss the physical implications, and the similarity/differences with a theory of BCS pairing with phase fluctuations.
Recent experiments on twisted bilayer graphene have shown a high-temperature parent state with massless Dirac fermions and broken electronic flavor symmetry; superconductivity and correlated insulators emerge from this parent state at lower temperatures. We propose that the superconducting and correlated insulating orders are connected by Wess-Zumino-Witten terms, so that defects of one order contain quanta of another order and skyrmion fluctuations of the correlated insulator are a "mechanism" for superconductivity. We present a comprehensive listing of plausible low-temperature orders, and t…
When a Mott metal-insulator transition is inhibited by a small amount of disorder in the layered dichalcogenide 1T-TaS$_2$, an inhomogeneous superconducting state arises below T=2.1 K, and coexists with a nearly-commensurate charge-density-wave. By angle-resolved photoelectron spectroscopy (ARPES) we show that it emerges from a bad metal state with strongly damped quasiparticles. Superconductivity is almost entirely suppressed by an external magnetic field of 0.1 T.
We present a novel route for attaining unconventional superconductivity (SC) in a strongly correlated system without doping. In a simple model of a correlated band insulator (BI) at half-filling we demonstrate, based on a generalization of the projected wavefunctions method, that SC emerges when e-e interactions and the bare band-gap are both much larger than the kinetic energy, provided the system has sufficient frustration against the magnetic order. As the interactions are tuned, SC appears sandwiched between the correlated BI followed by a paramagnetic metal on one side, and a ferrimagneti…
Metal-insulator transitions (MIT) belong to a class of fascinating physical phenomena, which includes superconductivity, and colossal magnetoresistance (CMR), that are associated with drastic modifications of electrical resistance. In transition metal compounds, MIT are often related to the presence of strong electronic correlations that drive the system into a Mott insulator state. In these systems the MIT is usually tuned by electron doping or by applying an external pressure. However, it was noted recently that a Mott insulator should also be sensitive to other external perturbations such a…
Paired valence electrons forming covalent bonds in molecues are confined cooper pair correlations. High pressure dissociates molecules in solid H2S, SiH4, H2 etc. and form extended structures. However, valence electrons are resilient and continue to bond and sometimes resonate. It is suggested that some structures contain emergent Mott insulators (EMI) and support superconductivity and other phases, under special conditions. In pressurized solid H2S, we propose presence of a sublattice of relatively narrow, nearly half filled band of H atoms, trapped in ordered interstitials of colvalently bon…
We study the insulating phase of disordered indium oxide films that undergo a field-tuned superconductor-insulator transition. The transport measurements in a perpendicular magnetic field show distinct regimes of strongly fluctuating order-parameter amplitude and phase, and reveal a wide range of insulator strength in samples with differing disorder, despite the similarity in behavior near the SIT. We characterize the strength of the insulating phase and compare it to the superconducting strength. We find that the films do not return to the expected normal state even at high perpendicular magn…
This article reviews recent results of magnetotransport and magnetization measurements performed on highly oriented pyrolitic graphite (HOPG) and single crystalline Kish graphite samples. Both metal-insulator and insulator-metal transitions driven by magnetic field applied perpendicular to the basal planes of graphite were found and discussed in the light of relevant theories. The results provide evidence for the existence of localized superconducting domains in HOPG even at room temperature, as well as an interplay between superconducting and ferromagnetic correlations. We also present experi…
Routes to enhance superconducting instability are explored for doped Mott insulators. With the help of insights for criticalities of metal-insulator transitions, geometrical design of lattice structure is proposed to control the instability. A guideline is to explicitly make flat band dispersions near the Fermi level without suppressing two-particle channels. In a one-dimensional model, numerical studies show that our prescription with finite-ranged hoppings realizes large enhancement of spin-gap and pairing dominant regions. We also propose several multi-band systems, where the pairing is dri…
Possible superconductivity in recently discovered (Tl,K)Fe$_x$Se$_2$ compounds is studied from the viewpoint of doped Mott insulator. The Mott insulating phase is examined to be preferred in the parent compound at $x=1.5$ due to the presence of Fe vacancies. Partial filling of vacancies at the Fe-sites introduces electron carriers and leads to electron doped superconductivity. By using a two-orbital Hubbard model in the strong coupling limit, we find that the s-wave pairing is more favorable at small Hund's coupling, and d$_{x^2-y^2}$ wave pairing is more favorable at large Hund's coupling.
We propose a class of wave functions that provide a unified description of antiferromagnetism and d-wave superconductivity in (doped) Mott insulators. The wave function has a Jastrow form and prohibits double occupancies. In the absence of holes, the wave function describes antiferromagnetism accurately. Off diagonal long range order develops at finite doping and the superconducting order parameter has d-wave symmetry. We also show how nodal quasiparticles and neutral spin excitations can be constructed from this wave function.
We have studied the charge dynamics of Sr-doped La2CuO4 at hole concentration p =0.07. We observed a clear indication of the competition between two new characteristic collective modes of the Wigner lattice orders suggested earlier: one corresponds to a Tc =15 K superconductivity and the other to Tc =30 K. Our results naturally explain the recent observation of metallic transport in extremely low (1%) Sr-doped La2CuO4 and establish a novel insulator to metal transition mechanismand superconductivity in the two-dimensional Wigner lattice ground state. We suggest that the fluctuations of the rel…
Near a Mott transition, strong electron correlations may enhance Cooper pairing. This is demonstrated in the Dynamical Mean Field Theory solution of a twofold-orbital degenerate Hubbard model with inverted Hund's rules on-site exchange, which favors local spin-singlet configurations. Close to the Mott insulator, which is a local version of a valence bond insulator, a pseudogap non-Fermi-liquid metal, a superconductor, and a normal metal appear, in striking similarity with the physics of the cuprates. The strongly correlated superconducting state has a larger Drude weight than the corresponding…
Magnetotransport of superconducting Nd_{2-x}Ce_xCuO_{4+y} (NdCeCuO) films is studied in the temperature interval 0.3-30 K. The microscopic theory of the quantum corrections to conductivity, both in the Cooper and in the diffusion channels, qualitatively describes the main features of the experiment including the negative magnetoresistance in the high field limit. Comparison with the model of the field-induced superconductor-insulator transition (SIT) is included and a crossover between these two theoretical approaches is discussed.
Quasi-two-dimensional layered BiSe, a natural super-lattice with Bi2Se3-Bi2-Bi2Se3 units, has recently been predicted to be a dual topological insulator, simultaneously weak topological insulator as well as topological crystalline insulator. Here using structural, transport, spectroscopic measurements and density functional theory calculations, we show that BiSe exhibits rich phase diagram with the emergence of superconductivity with Tc ~8K under pressure. Sequential structural transitions into SnSe-type energetically tangled orthorhombic and CsCl-type cubic structures having distinct supercon…
Quantum antiferromagnets on geometrically frustrated lattices often allow a number of unusual paramagnetic ground states. The fate of these Mott insulators upon doping is an important issue that may shed some light on the high $T_c$ cuprate problem. We consider the doped Mott insulator on the Shastry-Sutherland lattice via the t-J model. The U(1) slave-boson mean field theory reveals the strong competition between different broken symmetry states. It is found that, in some ranges of doping, there exist superconducting phases with or without coexisting translational-symmetry- breaking orders su…
Conventional Hartree-Fock mean field theory is used, for the first time, to investigate the full two-dimensional t-J model. To date, all other nontrivial mean field approaches modify the Hamiltonian or violate the double occupancy constraint. Unlike conventional mean field theory, these methods do not give variational results for the t-J model. The mean field phase diagram of the t-J model predicts enhanced superconductivity at the crossover between an insulating phase at low doping and a metallic phase at moderate doping. This behavior is remarkably similar to that of high temperature superco…
We investigate by electrical transport the field-induced superconducting state (FISC) in the organic conductor $λ$-(BETS)$_2$FeCl$_4$. Below 4 K, antiferromagnetic-insulator, metallic, and eventually superconducting (FISC) ground states are observed with increasing in-plane magnetic field. The FISC state survives between 18 and 41 T, and can be interpreted in terms of the Jaccarino-Peter effect, where the external magnetic field {\em compensates} the exchange field of aligned Fe$^{3+}$ ions. We further argue that the Fe$^{3+}$ moments are essential to stabilize the resulting singlet, two-dimen…
Topological Chiral Superconductivity from Doping Correlated Charge Transfer Insulator with Orbital Magnetism
Great Bay Institute for Advanced Study, Great Bay University（大湾区先进科技学院）；Great Bay University（大湾区大学）；Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China（中国科学院微观尺度物理科学国家研究中心及中国科学技术大学物理科学学院）
We investigate the potential existence of a superconducting phase in $5d$ Mott insulators with an eye to hole doped Sr$_2$IrO$_4$. Using a mean-field method, a mixed singlet-triplet superconductivity, $d + p$, is observed due to the antisymmetric exchange originating from a quasi-spin-orbit-coupling. Our calculation on ribbon geometry shows possible existence of the topologically protected edge states, because of nodal structure of the superconducting gap. These edge modes are spin polarized and emerge as zero-energy flat bands, supporting a symmetry protected Majorana states, verified by eval…
Superconductivity has been induced in insulating ultra-thin films of amorphous bismuth using the electric field effect. The screening of electron-electron interaction was found to increase with electron concentration in a manner correlated with the tendency towards superconductivity. This does not preclude an increase in the density of states being important in the development of superconductivity. The superconductor-insulator transition appears to belong to the universality class of the three dimensional XY model.
We theoretically study superconductivity in UTe$_2$, which is a recently-discovered strong candidate for an odd-parity spin-triplet superconductor. Theoretical studies for this compound faced difficulty because first-principles calculations predict an insulating electronic state, incompatible with superconducting instability. To overcome this problem, we take into account electron correlation effects by a GGA$+U$ method and show the insulator-metal transition by Coulomb interaction. Using Fermi surfaces obtained as a function of $U$, we clarify topological properties of possible superconductin…
Using the variational cluster approach based on the self-energy functional theory, we study the possible occurrence of excitonic order and superconductivity in the two-orbital Hubbard model with intra- and inter-orbital Coulomb interactions. It is known that an antiferromagnetic Mott insulator state appears in the regime of strong intra-orbital interaction, a band insulator state appears in the regime of strong inter-orbital interaction, and an excitonic insulator state appears between them. In addition to these states, we find that the $s^{\pm}$-wave superconducting state appears in the small…
The antiferromagnetic(AFM) insulator-superconductor transition has been always a center of interest in the underlying physics of unconventional superconductors. The quantum phase transition between Mott insulator with AFM and superconductor can be induced by doping charge carriers in high-Tc cuprate superconductors. For the best characterized organic superconductors of k-(BEDT-TTF)2X (X=anion), a first order transition between AFM insulator and superconductor can be tuned by applied external pressure or chemical pressure. Also, the superconducting state can be directly developed from AFM insul…
Recent discoveries, as well as open questions, in experimentally realized correlated electron materials are reviewed. In particular, high temperature superconductivity in the cuprates and in the recently discovered iron pnictides, possible chiral p-wave superconductivity in strontium ruthenate, the search for quantum spin liquid behavior in real materials, and new experimental discoveries in topological insulators are discussed.
We explore the ground-state properties of the two-band Hubbard model with degenerate electronic bands, parametrized by nearest-neighbor hopping $t$, intra- and inter-orbital on-site Coulomb repulsions $U$ and $U^\prime$, and Hund coupling $J$, focusing on the case with $J>0$. Using Jastrow-Slater wave functions, we consider both states with and without magnetic/orbital order. Electron pairing can also be included in the wave function, in order to detect the occurrence of superconductivity for generic electron densities $n$. When no magnetic/orbital order is considered, the Mott transition is c…
High-temperature superconductors at zero doping can be considered strongly correlated two-dimensional Mott insulators. The understanding of the connection between the superconductor and the Mott insulator hits at the heart of the high-temperature superconducting mechanism. In this paper we investigate the zero-temperature doping-driven evolution of a superconductor towards the Mott insulator in a two dimensional electron model, relevant for high temperature superconductivity. To this purpose we use a cluster extension of dynamical mean field theory. Our results show that a standard (BCS) d-wav…
The most intriguing observation of cuprate experiments is most likely the metal-insulator-crossover (MIC), seen in the underdome region of the temperature-doping phase diagram of copper-oxides under a strong magnetic field, when the superconductivity is suppressed. This MIC, which results in such phenomena as heat conductivity downturn, anomalous Lorentz ratio, nonlinear entropy, insulating ground state, nematicity- and stripe-phases and Fermi pockets, reveals the nonconventional dielectric property of the pseudogap-normal phase. Since conventional superconductivity appears from a conducting n…
The high-temperature superconductivity in copper oxides emerges when carriers are doped into the parent Mott insulator. This well-established fact has, however, eluded a microscopic explanation. Here we show that the missing link is the self-energy pole in the energy-momentum space. Its continuous evolution with doping directly connects the Mott insulator and high-temperature superconductivity. We show this by numerically studying the extremely small doping region close to the Mott insulating phase in a standard model for cuprates, the two-dimensional Hubbard model. We first identify two relev…
Superconductors derived from topological insulators and topological crystalline insulators by doping have long been considered to be candidates as topological superconductors. Pb$_{0.5}$Sn$_{0.5}$Te is a topological crystalline insulator with mirror symmetry protected surface states on (001), (011) and (111) oriented surfaces. The superconductor (Pb$_{0.5}$Sn$_{0.5}$)$_{0.7}$In$_{0.3}$Te is induced by In doping in Pb$_{0.5}$Sn$_{0.5}$Te, and is thought to be a topological superconductor. Here we report the first scanning tunneling spectroscopy measurement of the superconducting state as well a…
Superconductivity emerges from the cuprate antiferromagnetic Mott state with hole doping. The resulting electronic structure is not understood, although changes in the state of oxygen atoms appear paramount. Hole doping first destroys the Mott state yielding a weak insulator where electrons localize only at low temperatures without a full energy gap. At higher doping, the 'pseudogap', a weakly conducting state with an anisotropic energy gap and intra-unit-cell breaking of 90\degree-rotational (C4v) symmetry appears. However, a direct visualization of the emergence of these phenomena with incre…
Copper oxides become superconductors rapidly upon doping with electron holes, suggesting a fundamental pairing instability. The Cooper mechanism explains normal superconductivity as an instability of a fermi-liquid state, but high-temperature superconductors derive from a Mott-insulator normal state, not a fermi liquid. We show that precocity to pair condensation with doping is a natural property of competing antiferromagnetism and d-wave superconductivity on a singly-occupied lattice, thus generalizing the Cooper instability to doped Mott insulators, with significant implications for the high…
We investigate a two-orbital model for iron-based superconductors to elucidate the effect of interplay between electron correlation and Jahn-Teller electron-phonon coupling by using the dynamical mean-field theory combined with the exact diagonalization method. When the intra- and inter-orbital Coulomb interactions, $U$ and $U'$, increase with $U=U'$, both the local spin and orbital susceptibilities, $χ_{s}$ and $χ_{o}$, increase with $χ_{s}=χ_{o}$ in the absence of the Hund's rule coupling $J$ and the electron-phonon coupling $g$. In the presence of $J$ and $g$, there are distinct two regimes…
Intrinsic topological superconductors with p-wave pairing are rare in nature. Its underlying reason is due to the fact that it is usually difficult to change the relative strength between the singlet and triplet channels for the electron-electron interaction in material. Here we show that by considering superconductivity occurring on surfaces of topological insulators (TIs), the relative strength between the singlet and triplet channels can be changed by geometry and sizes of TIs. Specifically, we show that pairing of electrons at different locations on the surface of a topological insulator g…
The effect of proximity to a Mott insulating phase on the charge transport properties of a superconductor is determined. An action describing the low energy physics is formulated and different scenarios for the approach to the Mott phase are distinguished by different variation with doping of the parameters in the action. A crucial issue is found to be the doping dependence of the quasiparticle charge which is defined here and which controls the temperature and field dependence of the electromagnetic response functions. Presently available data on high-T$_{c}$ superconductors are analysed. The…
When bilayer graphene is rotationally faulted to an angle $θ\approx 1.1^\circ$, theory predicts the formation of a flat electronic band and correlated insulating, superconducting, and ferromagnetic states have all been observed at partial band filling. The proximity of superconductivity to correlated insulators has suggested a close relationship between these states, reminiscent of the cuprates where superconductivity arises by doping a Mott insulator. Here, we show that superconductivity can appear without correlated insulating states. While both superconductivity and correlated insulating be…
Strontium intercalation between van der Waals bonded layers of topological insulator Bi2Se3 is found to induce superconductivity with a maximum Tc of 2.9 K. Transport measurement on single crystal of optimally doped sample Sr0.1Bi2Se3 shows weak anisotropy (1.5) and upper critical field Hc2(0) equals to 2.1 T for magnetic field applied per-pendicular to c -axis of the sample. The Ginzburg-Landau coherence lengths are Xi-ab = 15.3 Å and Xi_c = 10.2 Å. The lower critical field and zero temperature penetration depth Lambda(0) are estimated to be 0.35 mT and 1550 nm respectively. Hall and Seebeck …
We propose a phenomenological understanding of the recently discovered weak Mott insulator in the moiré superlattice of twisted bilayer graphene, especially the emergent superconductivity at low temperature within the weak Mott insulator phase, namely while lowering temperature, the longitudinal resistivity first grows below temperature $T_m$, but then rapidly drops to zero at even lower temperature $T_c$. An emergent superconductor in an insulator phase is very unusual. Here we propose that this phenomenon is due to the pure two-dimensional nature of the bilayer graphene moiré superlattice. W…
High-temperature superconductivity emerges in the CuO$_2$ plane upon doping a Mott insulator. To ascertain the influence of Mott physics plus short-range correlations, we solve a three-band copper-oxide model in the charge-transfer regime using cellular dynamical mean-field theory with continuous-time quantum Monte Carlo as an impurity solver. We report the normal and superconducting phase diagram of this model as a function of doping, interaction strength and temperature. Upon hole doping of the charge-transfer insulator, the phase boundary between pseudogap and correlated metal consists of a…
Current theories of superfluidity are based on the idea of a coherent quantum state with topologically protected, quantized circulation. When this topological protection is absent, as in the case of $^3$He-A, the coherent quantum state no longer supports persistent superflow. Here we argue that the loss of topological protection in a superconductor gives rise to an insulating ground state. We specifically introduce the concept of a Skyrme insulator to describe the coherent dielectric state that results from the topological failure of superflow carried by a complex vector order parameter. We ap…
Binary ruthenium pnictides, RuP and RuAs, with an orthorhombic MnP structure, were found to show a metal to a non-magnetic insulator transition at TMI = 270 K and 200 K, respectively. In the metallic region above TMI, a structural phase transition, accompanied by a weak anomaly in the resistivity and the magnetic susceptibility, indicative of a pseudo-gap formation, was identified at Ts = 330 K and 280 K, respectively. These two transitions were suppressed by substituting Ru with Rh. We found superconductivity with a maximum Tc = 3.7 K and Tc =1.8 K in a narrow composition range around the cri…
We introduce and analyze a model that sheds light on the interplay between correlated insulating states, superconductivity, and flavor-symmetry breaking in magic angle twisted bilayer graphene. Using a variational mean-field theory, we determine the normal-state phase diagram of our model as a function of the band filling. The model features robust insulators at even integer fillings, occasional weaker insulators at odd integer fillings, and a pattern of flavor-symmetry breaking at non-integer fillings. Adding a phonon-mediated inter-valley retarded attractive interaction, we obtain strong-cou…
In the last two decades there have been tremendous attempts to built an adequate theory of high-temperature superconductivity. Most studies (including our efforts) used some model Hamiltonians with input parameters not directly related to the material. The dielectric response function of electrons in strongly correlated high-temperature superconductors is apriori unknown. Hence one has to start with the generic Hamiltonian including unscreened Coulomb and Froehlich electron-phonon interactions operating on the same scale since any ad-hoc assumption on their range and relative magnitude might f…
The surface of a 3D topological insulator is conducting and the topologically nontrivial nature of the surface states is observed in experiments. It is the aim of this paper to review and analyze experimental observations with respect to the magnetotransport in Bi-based 3D topological insulators, as well as the superconducting transport properties of hybrid structures consisting of superconductors and these topological insulators. The helical spin-momentum coupling of the surface state electrons becomes visible in quantum corrections to the conductivity and magnetoresistance oscillations. An a…
Lacunar spinel GaTa$_4$Se$_8$ is a unique example of spin-orbit coupled Mott insulator described by molecular $j_{\text{eff}}\!=\!3/2$ states. It becomes superconducting at T$_c$=5.8K under pressure without doping. In this work, we show, this pressure-induced superconductivity is a realization of a new type topological phase characterized by spin-2 Cooper pairs. Starting from first-principles density functional calculations and random phase approximation, we construct the microscopic model and perform the detailed analysis. Applying pressure is found to trigger the virtual interband tunneling …
