Flat Bands and Enigma of Metamagnetic Quantum Critical Regime in Sr3Ru2O7

TL;DR

This paper explains the metamagnetic quantum criticality in Sr3Ru2O7 by linking it to fermion condensation and flat band formation, accounting for entropy peaks and resistivity jumps observed experimentally.

Contribution

It introduces a phase diagram model that unifies experimental features of Sr3Ru2O7 with fermion condensation theory, revealing the role of flat bands at quantum critical points.

Findings

Flat band formation explains entropy peaks.

Resistivity jumps are caused by flat band effects.

The phase diagram aligns with experimental observations.

Abstract

Understanding the nature of field-tuned metamagnetic quantum criticality in the ruthenate Sr3Ru2O7 has presented a significant challenge within condensed matter physics. It is known from experiments that the entropy within the ordered phase forms a peak, and is unexpectedly higher than that outside, while the magnetoresistivity experiences steep jumps near the ordered phase. We find a challenging connection between Sr3Ru2O7 and heavy-fermion metals expressing universal physics that transcends microscopic details. Our construction of the T-B phase diagram of Sr3Ru2O7 permits us to explain main features of the experimental one, and unambiguously implies an interpretation of its extraordinary low-temperature thermodynamic in terms of fermion condensation quantum phase transition leading to the formation of a flat band at the restricted range of magnetic fields B. We show that it is the flat band that generates both the entropy peak and the resistivity jumps at the QCPs.