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Register a new userBandwidth tuning triggers interplay of charge order and superconductivity in two-dimensional organic materials
تحقيق الحجم الفرعي يؤدي إلى تفاعل من الطلب الشحني والسوبركوندوكتيفيتي في المواد العضوية الثنائية الأبعاد.
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نحن نلاحظ الاهتزازات في النظام الطبقي الشحنة في الموصل السوبر كوازي-اثنين الأبعاد العضوي $beta^{primeprime}$-(BEDT-TTF)2 SF5 CH2 CF2 SO3 بواسطة الطيف الشفاف الصوتي، الذي يجري فحص النظام الطبقي الشحنة المتزامن، وباستخدام الطيف الشفاف الحراري للاستعراض الداخلي للمساحة. يقلل التفاعل الالكتروني الفعال في المعدن المنظم الهيكلي من الاهتزازات النظام الطبقي الشحنة والسوبر السلكي، مشيرا إلى تعاملهما معا. نحن نقارن نتائج تجاربنا مع الحسابات المطبقة على النموذج الهابرد الموسع.
We observe charge-order fluctuations in the quasi-two-dimensional organic superconductor $beta^{primeprime}$-(BEDT-TTF)2 SF5 CH2 CF2 SO3 both by means of vibrational spectroscopy, locally probing the fluctuating charge order, and investigating the in-plane dynamical response by infrared reflectance spectroscopy. The decrease of effective electronic interaction in an isostructural metal suppresses both charge-order fluctuations and superconductivity, pointing on their interplay. We compare the results of our experiments with calculations on the extended Hubbard model.
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We report comprehensive Raman and infrared investigations of charge-order (CO) fluctuations in the organic metal $beta^{primeprime}$-(BEDT-TTF)$_2$SF$_5$CHFSO$_3$ and superconductor $beta^{primeprime}$-(BEDT-TTF)$_2$SF$_5$CH$_2$CF$_2$SO$_3$. The charge-sensitive vibrational bands have been analyzed through an extension of the well-known Kubo model for the spectral signatures of an equilibrium between two states. At room temperature, both salts exhibit charge fluctuations between two differently charged molecular states with an exchange frequency of about $6times10^{11} {rm s}^{-1}$. The exchange rate of the metallic salt remains roughly constant down to 10 K, while in the superconductor the exchange velocity starts to decrease below 200 K, and a frozen charge-ordered state emerges, and coexists with the charge-order fluctuation state down to the superconducting temperature. These findings are confronted with other existing spectroscopic experiments, and a tentative phase diagram is proposed for the $beta^{primeprime}$ BEDT-TTF quarter-filled salts.
This review provides a perspective on recent developments and their implications for our understanding of novel quantum phenomena in the physics of two-dimensional organic solids. We concentrate on the phase transitions and collective response in the charge sector, the importance of coupling of electronic and lattice degrees of freedom and stress an intriguing role of disorder. After a brief introduction to low-dimensional organic solids and their crystallographic structures, we focus on the dimensionality and interactions and emergent quantum phenomena. Important topics of current research in organic matter with sizeable electronic correlations are Mott metal-insulator phase transitions, charge order and ferroelectricity. Highly frustrated two-dimensional systems are established model compounds for studying the quantum spin liquid state and the competition with magnetic long-range order. There are also unique examples of quantum disordered state of magnetic and electric dipoles. Representative experimental results are complemented by current theoretical approaches.
HoTe$_{3}$, a member of the rare-earth tritelluride ($R$Te$_{3}$) family, and its Pd-intercalated compounds, Pd$_x$HoTe$_{3}$, where superconductivity (SC) sets in as the charge-density wave (CDW) transition is suppressed by the intercalation of a small amount of Pd, are investigated using angle-resolved photoemission spectroscopy (ARPES) and electrical resistivity. Two incommensurate CDWs with perpendicular nesting vectors are observed in HoTe$_{3}$ at low temperatures. With a slight Pd intercalation ($x$ = 0.01), the large CDW gap decreases and the small one increases. The momentum dependence of the gaps along the inner Fermi surface (FS) evolves from orthorhombicity to near tetragonality, manifesting the competition between two CDW orders. At $x$ = 0.02, both CDW gaps decreases with the emergence of SC. Further increasing the content of Pd for $x$ = 0.04 will completely suppress the CDW instabilities and give rise to the maximal SC order. The evolution of the electronic structures and electron-phonon couplings (EPCs) of the multiple CDWs upon Pd intercalation are carefully scrutinized. We discuss the interplay between multiple CDW orders, and the competition between CDW and SC in detail.
Actinide materials play a special role in condensed matter physics, spanning behaviours of itinerant d-electron and localized 4f-electron materials. An intermediate state, found notably in Pu-based materials whose 5f electrons are neither fully localized nor itinerant, is particularly challenging to understand. Superconductivity appearing in some actinide materials provides clues to the nature of the 5f electrons. PuCoGa5, the first Pu-based superconductor, is superconducting at Tc=18.5 K. This relatively high Tc is unprecedented in any other actinide system but is typical of itinerant electron compounds in which superconductivity is mediated by phonons. Recent studies of PuCoGa5 show that its superconductivity is not phonon-mediated; rather, these experiments are consistent with superconductivity produced by antiferromagnetic fluctuations of nearly localized 5f electrons. Similarities of PuCoGa5 with the superconducting and normal states of isostructural 4f analogues CeMIn5 (M=Co, Rh, Ir) and high-Tc cuprates enable new perspectives on the 5f electrons of Pu.
As superconductors are thinned down to the 2D limit, their critical temperature $T_c$ typically decreases. Here we report the opposite behavior, a substantial enhancement of $T_c$ with decreasing thickness, in 2D crystalline superconductor 2H-TaS$_2$. Remarkably, in the monolayer limit, $T_c$ increases to 3.4 K compared to 0.8 K in the bulk. Accompanying this trend in superconductivity, we observe suppression of the charge-density wave (CDW) transition with decreasing thickness. To explain these trends, we perform electronic structure calculations showing that a reduction of the CDW amplitude results in a substantial increase of the density of states at the Fermi energy, which contributes to the enhancement of $T_c$. Our results establish ultra-thin 2H-TaS$_2$ as an ideal platform to study the competition between CDW order and superconductivity.
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