Magnetic-thermodynamic phase transition in strained phosphorous-doped graphene

TL;DR

This study investigates a strain-induced magnetic-thermodynamic phase transition in phosphorous-doped graphene, revealing a tunable switch between magnetic and non-magnetic phases with distinct thermodynamic signatures.

Contribution

It introduces a novel strain-controlled magnetic quantum phase transition in P-doped graphene and analyzes its thermodynamic effects at finite temperatures.

Findings

Magnetic phase characterized by out-of-plane hybridization switches to non-magnetic in-plane hybridization.

Electronic entropy and specific heat exhibit a $\\Lambda$-shaped profile around the transition point.

Thermodynamic quantities sharply change at critical strain values, indicating a controllable magnetic switch.

Abstract

We explore quantum-thermodynamic effects in a phosphorous (P)-doped graphene monolayer subjected to biaxial tensile strain. Introducing substitutional P atoms in the graphene lattice generates a tunable spin magnetic moment controlled by the strain control parameter $\varepsilon$. This leads to a magnetic quantum phase transition (MQPT) at zero temperature modulated by $\varepsilon$. The system transitions from a magnetic phase, characterized by an out-of-plane $sp^3$ type hybridization of the P-carbon (P-C) bonds, to a non-magnetic phase when these bonds switch to in-plane $sp^2$ hybridization. Employing a Fermi-Dirac statistical model, we calculate key thermodynamic quantities as the electronic entropy $S_e$ and electronic specific heat $C_e$. At finite temperatures, we find the MQPT is reflected in both $S_e$ and $C_e$, which display a distinctive $\Lambda$-shaped profile as a function of $\varepsilon$. These thermodynamic quantities sharply increase up to $\varepsilon = 5\% $ in the magnetic regime, followed by a sudden drop at $\varepsilon = 5.5\% $, transitioning to a linear dependence on $\varepsilon$ in the nonmagnetic regime. Notably, $S_e$ and $C_e$ capture the MQPT behavior for low and moderate temperature ranges, providing insights into the accessible electronic states in P-doped graphene. This controllable magnetic-to-nonmagnetic switch offers potential applications in electronic nanodevices operating at finite temperatures.