arXiv subjects

Matthew E. Matzelle

Publications and source records attributed to Matthew E. Matzelle.

3 recordsLinked to original sources

arXiv2024

Second Dome of Superconductivity in YBa$_2$Cu$_3$O$_7$ at High Pressure

Evidence is growing that a second dome of high-$T_\mathrm{c}$ superconductivity can be accessed in the cuprates by increasing the doping beyond the first dome. Here we use \emph{ab initio} methods without invoking any free parameters, such as the Hubbard $U$, to reveal that pressure could turn YBa$_2$Cu$_3$O$_7$ into an ideal candidate for second-dome-superconductivity, displaying the predicted signature of strongly hybridized $d_{x^2-y^2}$ and $d_{z^2}$ orbitals. Notably, pressure is found to induce a phase transition replacing the antiferromagnetic phases with an orbitally-degenerate $d$--$d$ phase. Our study suggests that the origin of the second dome is correlated with the oxygen-hole fraction in the CuO$_2$ planes and the collapse of the pseudogap phase.

cond-mat.supr-con↗

arXiv2017

Finite-Volume Corrections to Electromagnetic Masses for Larger-Than-Physical Electric Charges

The numerical value of the fine-structure constant generally leads to small isospin-breaking effects due to electromagnetism in QCD. This smallness complicates determining isospin breaking from lattice QCD computations that include electromagnetism. One solution to this problem consists of performing computations using larger-than-physical values of the electric charge, and subsequently extrapolating (or interpolating) to the physical value of the fine-structure constant. Motivated by recent lattice QCD + QED computations of electromagnetic masses employing this setup, we consider finite-volume effects arising from the use of larger-than-physical electric charges. A modified power-counting scheme, which is based on treating the fine-structure constant as larger than its physical value, is explored. Results for perturbative QED corrections, however, are surprising. Within the framework of non-relativistic QED, multi-loop diagrams exhibit a momentum factorization property that produces exact cancellations. We determine that power-law finite-volume effects vanish at the leading two- and three-loop order, as well as the next-to-leading two-loop order. For larger-than-physical charges, we consequently expect no appreciable volume corrections beyond leading-order QED.

hep-lat↗

arXiv2015

Low-Energy QCD in the Delta Regime

We investigate properties of low-energy QCD in a finite spatial volume, but with arbitrary temperature. In the limit of small temperature and small cube size compared to the pion Compton wavelength, Leutwyler has shown that the effective theory describing low-energy QCD reduces to that of quantum mechanics on the coset manifold, which is the so-called delta regime of chiral perturbation theory. We solve this quantum mechanics analytically for the case of a $U(1)_L \times U(1)_R$ subgroup of chiral symmetry, and numerically for the case of $SU(2)_L \times SU(2)_R$. We utilize the quantum mechanical spectrum to compute the mass gap and chiral condensate, and investigate symmetry restoration in a finite spatial volume as a function of temperature. Because we obtain the spectrum for non-zero values of the quark mass, we are able to interpolate between the rigid rotor limit, which emerges at vanishing quark mass, and the harmonic approximation, which is referred to as the p-regime. We find that the applicability of perturbation theory about the rotor limit largely requires lighter-than-physical quarks. As a stringent check of our results, we raise the temperature to that of the inverse cube size. When this condition is met, the quantum mechanics reduces to a matrix model. The condensate we obtain in this limit agrees with that determined analytically in the epsilon regime.

hep-lat↗