Non Fermi liquid signatures across strain engineered metal-insulator transition in line-graph lattices

Abstract

Controlling the properties and thus the functionalities of correlated electron systems via externally tunable perturbations has always remained a cherished goal in quantum condensed matter physics. Recently, straintronics has proved to be one such external control which can dictate the quantum phases and transitions in materials via the reconstruction of their electronic band structure. A particularly intriguing scenario arises in the context of flat band line-graph lattices wherein straintronics is found to bring forth non trivial phase transitions. This paper reports the phase transitions and thermal scales across the Lieb/Kagome interconversion in the electronic interaction-strain-temperature space. Based on the thermodynamic, spectroscopic and transport signatures across the strain tuned interconversion of these line-graph lattices we have mapped out the low temperature phases and thermal transition scales, numerically determined using non perturbative calculations. While at the low temperatures, interaction-strain plane is spanned by magnetically correlated insulators, flat band induced weak transiently localized insulators and non Fermi liquid metallic phases, thermal fluctuations aid in to stabilize coexistent magnetic correlations. Apart from quantifying the magnetic transition scales in this system our results on the spectroscopic and transport signatures distill the strain tuned metal-insulator transition and crossover scales which exhibit variable transport scaling exponents.

Figures (11)

• Figure 1: Static magnetic structure factor ($S({\bf q})$) at $T=0.01t$ for selected $U-\eta$ cross sections. At large strain, magnetic correlations set in for $U>3t$, the intermediate interaction $U=3.8t$ hosts a precursor Coulomb phase while the strong coupling regime ($U=4.4t$ and $U=6.0t$) is characterized by a Coulomb phase.
• Figure 2: Strain dependence of the NN ($\langle {\bf m}_{i} .{\bf m}_{j}\rangle$) and the NNN ($\langle {\bf m}_{i}.{\bf m}_{k}\rangle$) correlations at selected interactions, at $T=0.01t$. A positive sign of the magnitude indicates the FM correlation while the AF correlation is characterized by the negative sign.
• Figure 3: Spectral function ($A({\bf k}, \omega)$) maps at $T=0.01t$ and selected $U-\eta$ cross sections showing the band structure reconstruction across the Lieb/Kagome interconversion.
• Figure 4: Single particle DOS ($N(\omega)$) as a function of $\eta$ at selected interactions representative of: (a) weak ($U=3.0t$), (b-c) intermediate ($U=3.8t$, $U=4.4t$) and (d) strong ($U=6.0t$) coupling regimes, highlighting the strain controlled gap-gapless transition.
• Figure 5: (a)-(c): Strain dependence of the optical conductivity ($\sigma(\omega)$) at selected interactions, showing the NFL signatures in terms of the DDP and the intermediate frequency polaronic peak. (d) Variation of $\sigma(\omega)$ with interaction at the selected strain of $\eta = 0.6t$.