arXiv subjects

Felix A. Buot

Publications and source records attributed to Felix A. Buot.

13 recordsLinked to original sources

arXiv2026

On pseudogap phase as precursor to a superconducting dome in high-Tc cuprates: Non-analytic T* as a function of doping

We generalize the condition under which a quantum material exhibiting a pseudogap phase is a precursor to a superconducting (SC) dome. The result reveals the non-analytic T* as a function of doping. A well-known example is the high-Tc cuprates. Essentially, the SC dome is generated under two conditions: (1) that the pseudogap T* is a decreasing function of doping, due to the decrease in size of extended pairing of doped holes with doping, and most importantly, (2) that the rate of configurational-ordering parameter is an increasing function of doping as a result of the decrease in extended length of the disordered pairs. The theory behind these hinges on a novel strong entanglement and confinement hole pairing (ECHP) mechanism that unravels the microscopic features of the entire phase diagram of both electron and hole-doped high-Tc cuprates, recently discussed in the by Buot et al. The ECHP configurational ordering (CO) at the underdoped and overdoped regions qualitatively agrees with spin texture experiments, and strongly suggests that strange metal phase can only occur in the overdoped region, in agreement with experiments.

cond-mat.supr-con↗

arXiv2026

Entanglement and confinement: A new pairing mechanism in high-T_{C} cuprates

We demonstrate that entanglement and confinement hole pairing (ECHP) is a precise physics of the entanglement framework of the RVB theory of high-Tc cuprates. Our novel strong ECHP mechanism explains the entire phase diagram of both electron and hole-doped cuprates, notably the linearly decreasing T* at the pseudogap but with "T*-singularity" at the peak of the superconducting (SC) dome, the Tc=T* at the optimum doping and the rest of the overdoped regions of the SC dome, the duality of the spin gap and strange metal phase, the presence of the parallel superconducting stripes in the CuO plane (spin-polarized and spin-unpolarized channels), and the linear-T resistivity of the strange metal phase above the overdoped regions of the SC dome. This also explains the experimental spin textures of the cuprates. We refer to our new ECHP model as a resonating entanglement and confinement hole pair (RECHP) theory. Based on RECHP theory, we were able to provide a conceptual and comprehensive semiquantitative explanation of the entire phase diagram, thus providing the sought-after pairing mechanism responsible for the entire phase diagram of high-T_{C} cuprates.

cond-mat.supr-con↗

arXiv2023

An inverter-chain link implementation of quantum teleportation and superdense coding

A new perspective in terms of inverter-chain link (ICL) diagrams of quantum entanglement faithfully captures the fundamental concept of quantum teleportation and superdense coding. The ICL may be considered a series of σ_{x} Pauli-matrix operations, where a physical/geometric representation provides the mysterious link raised by EPR. Here, we employ discrete phase space and ICL analyses of quantum entanglement as a resource for quantum teleportation and superdense coding. We underscore the quantum superposition principle and Hadamard transformation under a local single-qubit operation. On the fundamental question posed by EPR, our result seems to lend support to the geometric nature of quantum entanglement. In concluding remarks, we discuss very briefly a bold conjecture in physics aiming to unify general relativity with quantum mechanics, namely, ER=EPR.

quant-ph↗

arXiv2023

On Entanglement Measures: Discrete Phase Space and Inverter-Chain Link Viewpoint

In contrast to abstract statistical analyses in the literature, we present a concrete physical diagrammatic model of entanglement characterization and measure with its underlying discrete phase-space physics. This paper serves as a pedagogical treatment of this complex subject of entanglement measures. We review the important inherent concurrence property of entangled qubits, as well as underscore its emergent qubit behavior. From the discrete phase space point of view, concurrence translates to translation symmetry of entangled binary systems in some quantitative measure of entanglement. Although the focus is on bipartite system, the notion is readily extendable to multi-partite system of qubits, as can easily be deduced from the physical inverter-chain link model. A diagrammatic analysis of the entanglement of formation for any multi-partite qubit system is given

quant-ph↗

arXiv2022

Dynamics of Functional Phase Space Distribution in QFT: A Third Quantization and Dynamical Unification of QFT and CMP

We proposed a third quantization scheme to derive the quantum dynamics of the functional phase space distribution in quantum field theory (QFT). The derivation is straightforward and algorithmic. This readily yields the ballistic quantum transport equation of QFT distribution in (p,q)- functional phase space, not in ordinary position-momentum (p,q)-space. Our starting point is the general mixed space representation in QFT. The end result serves as a unification of the quantum superfield transport theory of condensed matter physics (CMP) and QFT. This is summarized in a Table of correspondence. This third quantization scheme may have significance in quantum fluctuation theory of systems with many degrees of freedom. It may have relevance to cosmology: gravity, multi-universes, and Yang-Mills theory.

quant-ph↗

arXiv2022

Unification of Mixed Hilbert-Space Representations in Condensed Matter Physics and Quantum Field Theory

We present a unification of mixed-space quantum representations in Condensed Matter Physics (CMP) and Quantum Field Theory (QFT). The unifying formalism is based on being able to expand any quantum operator, for bosons, fermions, and spin systems, using a universal basis operator Y(u,v) involving mixed Hilbert spaces of P and Q, respectively, where P and Q are momentum and position operators in CMP (which can be considered as a bozonization of free Bloch electrons which incorporates the Pauli exclusion principle and Fermi-Dirac distribution), whereas these are related to the creation and annihilation operators in QFT, where ψ^{†}=-iP and ψ=Q. The expansion coefficient is the Fourier transform of the Wigner quantum distribution function (lattice Weyl transform) otherwise known as the characteristic distribution function. Thus, in principle, fermionization via Jordan-Wigner for spin systems, as well as the Holstein--Primakoff transformation from boson to the spin operators can be performed depending on the ease of the calculations. Unitary transformation on the creation and annihilation operators themselves is also employed, as exemplified by the Bogoliubov transformation. Moreover, whenever Y(u,v) is already expressed in matrix form, M_{ij}, e.g. the Pauli spin matrices, the Jordan--Schwinger transformation is a map to bilinear expressions of creation and annihilation operators which expedites computation of representations. We show that the well-known coherent states formulation of quantum physics is a special case of the present unification. A new formulation of QFT based on Q-distribution of functional-field variables is suggested. The case of nonequilibrium quantum transport physics, which not only involves non-Hermitian operators but also time-reversal symmetry breaking, is discussed in the Appendix.

quant-ph↗

arXiv2021

On quantum Hall effect: Covariant derivatives, Wilson lines, gauge potentials, lattice Weyl transforms, and Chern numbers

We show that the gauge symmetry of the nonequilibrium quantum transport of Chern insulator in a uniform electric field is governed by the Wilson line of parallel transport operator coupled with the dynamical translation operator. This is dictated by the minimal coupling of derivatives with gauge fields in U (1) gauge theory. This parallel transport symmetry consideration leads to the integer quantum Hall effect in electrical conductivity obtained to first-order gradient expansion of the nonequilibrium quantum transport equations.

cond-mat.mes-hall↗

arXiv2021

Nonequilibrium superfield and lattice Weyl transform transport approach to quantum Hall effect

We derive the topological Chern number of the integer quantum Hall effect in electrical conductivity, using Buot's superfield and lattice Weyl transform nonequilibrium quantum transport formalism. The method is naturally straightforward, appropriate for treating nonequilibrium systems acted on by external electromagnetic fields. We have identified the topological invariant in the effective (~p; ~q; E; t)-phase space via the nonequilibrium quantum transport equation, generally not to first-order in electric field but to first-order in the gradient expansion. We have also derive the Kubo current-current correlation for the Hall current as a by-product of our new transport approach. The Berry curvature related to orbital magnetic moment is also calculated.

cond-mat.mes-hall↗

arXiv2021

Comments on the Weyl-Wigner calculus for lattice models

Here, we clarify the physical aspects between the discrete Weyl-Wigner (W-W) formalism, well developed in condensed matter physics, and the so-called 'precise Weyl-Wigner calculus for lattice models' recently appearing in the literature. We point out that the use of compact continuous momentum space for a discrete lattice model is unphysically founded. It has an incommensurate phase space, highly unphysical, lacks the finite fields aspects, as exemplified by the Born-von Karman boundary condition of compactified Bravais lattice of solid-state physics, and leads to several ambiguities. This new W-W formalism simply lacks bijective Fourier transformation, which is well-known to support the uncertainty principle of canonical conjugate dynamical variables of quantum physics. Moreover, this new W-W formalism for lattice models failed to handle the quantum physics of qubits, representing two discrete lattice sites.

quant-ph↗

arXiv2020

On quantum Hall effect, Kosterlitz-Thouless phase transition, Dirac magnetic monopole, and Bohr-Sommerfeld quantization

We addressed quantization phenomena in transport and vortex/precession-motion of low-dimensional systems, stationary quantization of confined motion in phase space due to oscillatory dynamics or compacti fication of space and time for steady-state systems (e.g., particle in a box or torus, Brillouin zone, and Matsubara time zone or Matsubara quantized frequencies), and the quantization of sources. We discuss how the self-consistent Bohr-Sommerfeld quantization condition permeates the relationships between the quantization of integer Hall effect, fractional quantum Hall effect, the Berezenskii-Kosterlitz-Thouless vortex quantization, the Dirac magnetic monopole, the Haldane phase, contact resistance in closed mesoscopic circuits of quantum physics, and in the monodromy (holonomy) of completely integrable Hamiltonian systems of quantum geometry. In quantum transport of open systems, quantization occurs in fundamental units of quantum conductance, other closed systems in quantum units dictated by Planck's constant, and for sources in units of discrete vortex charge and Dirac magnetic monopole charge. The thesis of the paper is that if we simply cast the B-S quantization condition as a U(1) gauge theory, like the gauge field of the topological quantum field theory (TQFT) via the Chern-Simons gauge theory, or specifically as in topological band theory (TBT) of condensed matter physics in terms of Berry connection and curvature to make it self-consistent, then all the quantization method in all the physical phenomena treated in this paper are unified.

cond-mat.mes-hall↗

arXiv2019

Generalized Nonequilibrium Quantum Transport of Spin and Pseudospins: Entanglements and Topological Phases

General nonequilibrium quantum transport equations are derived for a coupled system of charge carriers, Dirac spin, isospin (or valley spin), and pseudospin, such as either one of the band, layer, impurity, and boundary pseudospins. Limiting cases are obtained for one, two or three different kinds of spin ocurring in a system. We show that a characteristic integer number $N_{s}$ determines the formal form of spin quantum transport equations, irrespective of the type of spins or pseudospins, as well as the maximal entanglement entropy. The results may shed a new perspective on the mechanism leading to zero modes and chiral/helical edge states in topological insulators, integer quantum Hall effect topological insulator (QHE-TI), quantum spin Hall effect topological insulator (QSHE-TI) and Kondo topological insulator (Kondo-TI). It also shed new light in the observed competing weak localization and antilocalization in spin-dependent quantum transport measurements. In particular, a novel mechanism of localization and delocalization, as well as the new mechanism leading to the onset of superconductivity in bilayer systems seems to emerge naturally from torque entanglements in nonequilibrium quantum transport equations of spin and pseudospins. Moreover, the general results may serve as a foundation for engineering approximations of the quantum transport simulations of spintronic devices based on graphene and other 2-D materials such as the transition metal dichalcogenides (TMDs), as well as based on topological materials exhibiting quantum spin Hall effects. The extension of the formalism to spincaloritronics and pseudo-spincaloritronics is straightforward.

cond-mat.mes-hall↗

arXiv2016

Magnetic Susceptibility of Dirac Fermions, Bi-Sb Alloys, Interacting Bloch Fermions, Dilute Nonmagnetic Alloys, and Kondo Alloys

Wide ranging interest in Dirac Hamiltomian is due to the emergence of novel materials, namely, graphene, topological insulators and superconductors, the newly-discovered Weyl semimetals, and still actively-sought after Majorana fermions in real materials. We give a brief review of the relativistic Dirac quantum mechanics and its impact in the developments of modern physics. The quantum band dynamics of Dirac Hamiltonian is crucial in resolving the giant diamagnetism of bismuth and Bi-Sb alloys. Quantitative agreement of the theory with the experiments on Bi-Sb alloys has been achieved, and physically meaningful contributions to the diamagnetism has been identified. We also treat relativistic Dirac fermion as an interband dynamics in uniform magnetic fields. For the interacting Bloch electrons, the role of translation symmetry for calculating the magnetic susceptibility avoids any approximation to second order in the field. The magnetic susceptibility of Hubbard model and those of Fermi liquids are readily obtained as limiting cases. The expressions for magnetic susceptibility of dilute nonmagnetic alloys give a firm theoretical foundation of the empirical formulas used in fitting experimental results. For completeness, the magnetic susceptibility of dilute magnetic or Kondo alloys is also given for high and low temperature regimes.

cond-mat.mes-hall↗

arXiv2012

Nonequilibrium Multi-Band Spin Quantum Transport Equations: Spin, Pseudo-Spin, and Total Charge Coupling

Using the superfield nonequilibrium Greens function technique, we derive the spatio-temporal spin magnetization quantum transport equations (SMQTEs) for a two-band model of semiconductors. The relevant variables are the real (Pauli-Dirac) spin, pseudo-spin, and the total charge. The results show that the multi-band real SMQTEs are coupled to the pseudo-spin magnetization transport equations by virtue of the presence of two additional discrete quantum labels besides the up and down real-spin indices, namely, the conduction and valence band quantum labels. The SMQTEs essentially consist of three group of terms describing the rate of change, namely, (1) a group of terms similar to the equation for particle quantum transport, i.e., with spin-independent transport parameters, (2) a group of terms describing various torques influencing the spin orientation and directional flow of spin magnetization correlations or phase-space magnetization density, and (3) a group of terms expressing the coupling of the real spin magnetization with the pseudo-spin magnetization. Self-consistently, the pseudo-spin magnetization equations incorporate the pseudo-spin/real spin coupling, as well as the pseudo-spin coupling to the total charge.

cond-mat.other↗