Melting of charge order in the low-temperature state of an electronic ferroelectric-like system
Nora Hassan, Komalavalli Thirunavukkuarasu, Zhengguang Lu, Dmitry Smirnov, E. I. Zhilyaeva, С.А. Торунова, Rimma N. Lyubovskaya, Natalia Drichko
Abstract
Abstract Strong electronic interactions can drive a system into a state with a symmetry breaking. Lattice frustration or competing interactions tend to prevent symmetry breaking, leading to quantum disordered phases. In spin systems frustration can produce a spin liquid state. Frustration of a charge degree of freedom also can result in various exotic states, however, experimental data on these effects is scarce. In this work we demonstrate how in a Mott insulator on a weakly anisotropic triangular lattice a charge ordered state melts on cooling down to low temperatures. Raman scattering spectroscopy finds that $$\kappa$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>κ</mml:mi> </mml:math> -(BEDT-TTF) $${}_{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> Hg(SCN) $${}_{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> Cl enters an insulating “dipole solid” state at $$T=30\,{\mathrm{K}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>T</mml:mi> <mml:mo>=</mml:mo> <mml:mn>30</mml:mn> <mml:mspace/> <mml:mi>K</mml:mi> </mml:mrow> </mml:math> , but below $$T=15\,{\mathrm{K}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>T</mml:mi> <mml:mo>=</mml:mo> <mml:mn>15</mml:mn> <mml:mspace/> <mml:mi>K</mml:mi> </mml:mrow> </mml:math> the order melts, while preserving the insulating energy gap. Based on these observations, we suggest a phase diagram relevant to other quantum paraelectric materials.