arXiv subjects

Ankush Chaubey

Publications and source records attributed to Ankush Chaubey.

3 recordsLinked to original sources

arXiv2026

From Quantum Dimers to the $π$-flux Toric Code via Deconfined Multicriticality

Two-dimensional Rokhsar-Kivelson (RK) dimer models on bipartite lattices are generally limited to translation-symmetry-broken dimer crystals. We introduce a tensor-product regularisation of the dimer Hilbert space that yields a qubit Hamiltonian interpolating from the RK model to the $π$-flux toric code, thereby accessing a deconfined $\mathbb{Z}_2$ topological liquid. In this framework, the $\mathbb{Z}_2$ liquid descends from a multicritical $U(1)$ spin liquid through condensation of a charge-2 Higgs field, thus avoiding confinement. Using iDMRG together with low-energy field theory, we determine a phase diagram containing two continuous quantum phase transitions -- a $3\mathrm{D}$ XY$^{\ast}$ transition between the $\mathbb{Z}_2$ liquid and the columnar/plaquette-VBS, and a quantum Lifshitz transition between two dimer crystals -- alongside a first-order transition between the staggered crystal and the $\mathbb{Z}_2$ liquid. Our field theory suggests a deconfined multicritical point described by an Abelian Higgs model with dynamical critical exponent, $z=2$, where the three transitions meet, highlighting the interplay of fractionalisation and emergent gauge fluctuations.

cond-mat.str-el↗

arXiv2025

Superconductivity in Spin-Orbit coupled SU(8) Dirac Fermions on Honeycomb lattice

We study superconducting (SC) phases that are naturally proximate to a spin-orbit coupled SU(8) Dirac semi-metal on a honeycomb lattice. This system, which offers enhanced low-energy symmetries, presents an interesting platform for realizing unconventional superconductivity in j=3/2 electrons. In particular, we find 72 superconducting charge-$2e$ fermion bilinears which, under classification of microscopic symmetries, lead to 12 different SCs -- four singlets, two doublets, and six triplets -- 7 of them are gapped and 5 are symmetry-protected nodal SCs. The strong spin-orbit coupling leads to locking of the spin of the Cooper pairs with real-space direction -- as is evident from the structure of the Cooper pair wave-functions -- leading to unusual non-unitary superconductors (even singlets), and with finite momentum pairing (for the triplets). This results, in many cases, in the magnitude of multiple pairing gaps being intricately dependent on the direction of the SC order-parameter. The present classification of SCs along with normal phases (Phys. Rev. B 108, 245106 (2023)) provides the complete list of naturally occurring phases in the vicinity of such a SU(8) Dirac semi-metal. This study allows for understanding the global phase diagram of such systems, stimulating further experimental work on candidate materials such as metallic halides (MX$_3$ with M=Zr, Hf, and X=Cl, Br). Further, it provides the starting point for the exploration of unconventional phase transitions in such systems.

cond-mat.str-el↗

arXiv2024

Variational wave-functions for correlated metals

We study a set of many-body wave-functions of Fermions that are naturally written using momentum space basis and allow for quantum superposition of Fermion occupancy, $\{n_{\bf k}\}$. This {enables} us to capture the fluctuations of the Fermi-surface {(FS)} -- the singularly most important signature of a metal. We bench-mark our results in one spatial dimensions (1D) to show that these wave-functions allow for quantitative understanding of the Tomonaga-Luttinger liquid (TLL); computations of certain correlators using them can in fact be extended to larger systems sizes compared to conventional exact diagonalization (ED) allowing for a more systematic comparison with bosonization techniques. Finally we show that this basis may be useful for obtaining fixed-point wave-function for strongly correlated metals {in dimensions greater that one}. In particular, we study the case of coherent (equal) superposition of elliptical FS {in continuum (2D) and on a} square lattice{. In case of the former, our variational wave-function systematically interpolates between the phenomenology of the Fermi liquid ground state, i.e., finite single-Fermion residue at a sharp FS, to a non-Fermi liquid (NFL) with zero residue. In the NFL the jump in $\langle n_{\bf k}\rangle$ at the FS is replaced by a point of inflection (similar to a 1D TLL) whose contour is consistent with the Luttinger Theorem. In case of the square lattice, we} find highly anisotropic distribution of the quasi-particle residue, which, at finite resolution has an uncanny resemblance to the Fermi-arcs{, albeit at zero temperature,} seen in the pseudo-gap state of the cuprates.

cond-mat.str-el↗