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All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Seebeck effect studies in the charge density wave state of organic conductor α-(BEDT–TTF) 2 KHg(SCN) 4

Angular, magnetic field and temperature dependence of the interlayer Seebeck effect of the multiband organic conductor $\alpha -{(\mathrm{BEDT}-\mathrm{TTF})}_{2}\mathrm{KHg}{(\mathrm{SCN})}_{4}$ is experimentally studied at temperatures down to 0.55 K and fields up to 31 T in a wide range of angles. The background magnetic field and angular component of the Seebeck effect as well as the magnetic quantum oscillations that originate from the closed Fermi surface orbits are analyzed. The background interlayer Seebeck effect components show that above certain tilt angle of the magnetic field and above the kink field there is another CDW state in $\alpha -{(\mathrm{BEDT}-\mathrm{TTF})}_{2}\mathrm{KHg}{(\mathrm{SCN})}_{4}$, between previously known CDW0 and CDWx states, in agreement with magnetoresistance and magnetization studies in this material. Our observations show that this state possesses some of the properties of the CDW0 state. The Fermi surface in the third CDW state is still reconstructed but less imperfectly nested as expected as this state develops above the kink field. The temperature dependence of the interlayer Seebeck effect reveals that this state is developed at temperatures below 3 K and at field orientations around the second AMRO maximum. In addition, for the first time, a detailed T - θ phase diagram of $\alpha -{(\mathrm{BEDT}-\mathrm{TTF})}_{2}\mathrm{KHg}{(\mathrm{SCN})}_{4}$ based purely on Seebeck effect measurements is presented. We find that other states and transitions, beside the CDW states, also exist in a given temperature and angular range that have not been previously reported. These observations change the whole picture about the transport processes in the organic conductor $\alpha -{(\mathrm{BEDT}-\mathrm{TTF})}_{2}\mathrm{KHg}{(\mathrm{SCN})}_{4}$ and allow to better understand the complex nature of the CDW order in this and similar compounds.

Physics↗
DOE OSTI2020

Materials Data on KHg by Materials Project

KHg is delta Molybdenum Boride-like structured and crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are two inequivalent K sites. In the first K site, K is bonded in a 7-coordinate geometry to eight Hg atoms. There are a spread of K–Hg bond distances ranging from 3.61–4.08 Å. In the second K site, K is bonded in a 7-coordinate geometry to seven Hg atoms. There are a spread of K–Hg bond distances ranging from 3.65–3.94 Å. There are two inequivalent Hg sites. In the first Hg site, Hg is bonded in a 9-coordinate geometry to seven K and two equivalent Hg atoms. There are one shorter (3.08 Å) and one longer (3.11 Å) Hg–Hg bond lengths. In the second Hg site, Hg is bonded in a 10-coordinate geometry to eight K and two equivalent Hg atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KHg(PO3)3 by Materials Project

KHg(PO3)3 crystallizes in the orthorhombic P2_12_12_1 space group. The structure is three-dimensional. K1+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of K–O bond distances ranging from 2.71–3.07 Å. Hg2+ is bonded to six O2- atoms to form HgO6 octahedra that share corners with six PO4 tetrahedra. There are a spread of Hg–O bond distances ranging from 2.31–2.52 Å. There are three inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent HgO6 octahedra and corners with two PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 51–56°. There are a spread of P–O bond distances ranging from 1.50–1.64 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent HgO6 octahedra and corners with two PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 54–58°. There are a spread of P–O bond distances ranging from 1.50–1.62 Å. In the third P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent HgO6 octahedra and corners with two PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 47–56°. There are a spread of P–O bond distances ranging from 1.50–1.63 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent K1+, one Hg2+, and one P5+ atom. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the third O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the fourth O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the fifth O2- site, O2- is bonded in a distorted single-bond geometry to one K1+, one Hg2+, and one P5+ atom. In the sixth O2- site, O2- is bonded in a distorted single-bond geometry to one K1+, one Hg2+, and one P5+ atom. In the seventh O2- site, O2- is bonded in a distorted single-bond geometry to one K1+, one Hg2+, and one P5+ atom. In the eighth O2- site, O2- is bonded in a 1-coordinate geometry to one K1+, one Hg2+, and one P5+ atom. In the ninth O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent K1+, one Hg2+, and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Giant Angular Nernst Effect in the Organic Metal α-(BEDT-TTF) 2 KHg(SCN) 4

We have detected a large Nernst effect in the charge density wave state of the multiband organic metal α-(BEDT-TTF) 2 KHg(SCN) 4 . We find that apart from the phonon drag effect, the energy relaxation processes that govern the electron–phonon interactions and the momentum relaxation processes that determine the mobility of the q1D charge carriers have a significant role in observing the large Nernst signal in the CDW state in this organic metal. The emphasised momentum relaxation dynamics in the low field CDW state (CDW 0 ) is a clear indicator of the presence of a significant carrier mobility that might be the main source for observation of the largest Nernst signal. The momentum relaxation is absent with increasing angle and magnetic field, i.e., in the high-field CDW state (CDW x ) as evident from the much smaller Nernst effect amplitude in this state. In this case, only the phonon drag effect and electron–phonon interactions are contributing to the transverse thermoelectric signal. Our findings advance and change previous observations on the complex properties of this organic metal.

36 MATERIALS SCIENCE↗