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Dive into the research topics where Ana Akrap is active.

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Featured researches published by Ana Akrap.


Nature Materials | 2008

From Mott state to superconductivity in 1T-TaS2

Balazs Sipos; Anna F. Kusmartseva; Ana Akrap; H. Berger; László Forró; Eduard Tutiš

The search for the coexistence between superconductivity and other collective electronic states in many instances promoted the discovery of novel states of matter. The manner in which the different types of electronic order combine remains an ongoing puzzle. 1T-TaS(2) is a layered material, and the only transition-metal dichalcogenide (TMD) known to develop the Mott phase. Here, we show the appearance of a series of low-temperature electronic states in 1T-TaS(2) with pressure: the Mott phase melts into a textured charge-density wave (CDW); superconductivity develops within the CDW state, and survives to very high pressures, insensitive to subsequent disappearance of the CDW state and, surprisingly, also the strong changes in the normal state. This is also the first reported case of superconductivity in a pristine 1T-TMD compound. We demonstrate that superconductivity first develops within the state marked by a commensurability-driven, Coulombically frustrated, electronic phase separation.


Physical Review B | 2012

Optical properties of Bi2Te2Se at ambient and high pressures

Ana Akrap; C. C. Homes; M. K. Tran; Alberto Ubaldini; J. Teyssier; Enrico Giannini; D. van der Marel; Philippe Lerch

The temperature dependence of the complex optical properties of the three-dimensional topological insulator Bi2Te2Se is reported for light polarized in the a-b planes at ambient pressure, as well as the effects of pressure at room temperature. This material displays a semiconducting character with a bulk optical gap of 300 meV at 295 K. In addition to the two expected infrared-active vibrations observed in the planes, there is additional fine structure that is attributed to either the removal of degeneracy or the activation of Raman modes due to disorder. A strong impurity band located at 200 cm^{-1} is also observed. At and just above the optical gap, several interband absorptions are found to show a strong temperature and pressure dependence. As the temperature is lowered these features increase in strength and harden. The application of pressure leads to a very abrupt closing of the gap above 8 GPa, and strongly modifies the interband absorptions in the mid-infrared spectral range. While ab initio calculations fail to predict the collapse of the gap, they do successfully describe the size of the band gap at ambient pressure, and the magnitude and shape of the optical conductivity.


Physical Review B | 2009

Phonon Anomaly in BaFe2As2

C. C. Homes; Ana Akrap; J. J. Tu; Linjun Li; G. H. Cao; X.A. Xu

The detailed optical properties of BaFe2As2 have been determined over a wide frequency range above and below the structural and magnetic transition at TN ≃ 138 K. A prominent in-plane infrared-active mode is observed at 253 cm (31.4 meV) at 295 K. The frequency of this vibration shifts discontinuously at TN ; for T < TN the frequency of this mode displays almost no temperature dependence, yet it nearly doubles in intensity. This anomalous behavior appears to be a consequence of orbital ordering in the Fe-As layers.


Physical Review B | 2014

Optical properties of BiTeBr and BiTeCl

Ana Akrap; J. Teyssier; Arnaud Magrez; Philippe Bugnon; Helmuth Berger; A. B. Kuzmenko; Dirk van der Marel

We present a comparative study of the optical properties-reflectance, transmission, and optical conductivity- and Raman spectra of two layered bismuth-tellurohalides BiTeBr and BiTeCl at 300 and 5 K, for light polarized in the a-b planes. Despite different space groups, the optical properties of the two compounds are very similar. Both materials are doped semiconductors, with the absorption edge above the optical gap which is lower in BiTeBr (0.62 eV) than in BiTeCl (0.77 eV). The same Rashba splitting is observed in the two materials. A non-Drude free carrier contribution in the optical conductivity, as well as three Raman and two infrared phonon modes, are observed in each compound. There is a dramatic difference in the highest infrared phonon intensity for the two compounds, and a difference in the doping levels. Aspects of the strong electron-phonon interaction are identified. Several interband transitions are assigned, among them the low-lying absorption beta which has the same value 0.25 eV in both compounds, and is caused by the Rashba spin splitting of the conduction band. An additional weak transition is found in BiTeCl, caused by the lower crystal symmetry.


Physical Review B | 2008

Collective charge excitations below the metal-to-insulator transition in BaVS3

Tomislav Ivek; Tomislav Vuletić; S. Tomić; Ana Akrap; Helmuth Berger; László Forró

The charge response in barium vanadium sulfide (BaVS3) single crystals is characterized by dc resistivity and low-frequency dielectric spectroscopy. A broad relaxation mode in the megahertz range with a huge dielectric constant of approximate to 10(6) emerges at the metal-to-insulator phase transition T-MI approximate to 67 K, weakens with lowering temperature, and eventually levels off below the magnetic transition T-chi approximate to 30 K. The mean relaxation time is thermally activated in a manner similar to the dc resistivity. These features are interpreted as signatures of the collective charge excitations characteristic for the orbital ordering that gradually develops below T-MI and stabilizes at long-range scale below T-chi.


Review of Scientific Instruments | 2015

Versatile setup for optical spectroscopy under high pressure and low temperature

M. K. Tran; Julien Levallois; Ana Akrap; J. Teyssier; A. B. Kuzmenko; Florence Lévy-Bertrand; Riccardo Tediosi; Mehdi Brandt; Philippe Lerch; Dirk van der Marel

We present an optical setup for spectroscopic measurements in the infrared and of Raman shift under high pressure and at low temperature. Using a membrane-driven diamond anvil cell, the pressure can be tuned in situ up to 20 GPa and the temperatures ranges from room temperature down to 18 K in transmission mode and 13 K in reflection mode. In transmission, the setup is entirely working under vacuum to reduce the water absorption features and obtain a higher spectral stability. Since the infrared throughput obtained with a thermal source is limited, the use of a synchrotron source allowed to enhance the performance, as illustrated with results obtained with various materials. The analysis of the reflectivity is adapted so that it benefits from ambient pressure data and produces quantitative optical conductivity curves that can be easily compared to the results at ambient pressure.


Inorganic Chemistry | 2015

Crystal Structure, Transport, and Magnetic Properties of an Ir6+ Compound Ba8Al2IrO14

L. Yang; A. Pisoni; Arnaud Magrez; Sergiy Katrych; Alla Arakcheeva; Bastien Dalla Piazza; Krunoslav Prsa; Jaćim Jaćimović; Ana Akrap; J. Teyssier; László Forró; Henrik M. Rønnow

The novel iridate Ba8Al2IrO14 was prepared as single crystals by self-flux method, thereby providing a rare example of an all-Ir(VI) compound that can be synthesized under ambient pressure conditions. The preparation of all-Ir(6+) iridate without using traditional high-pressure techniques has to our knowledge previously only been reported in Nd2K2IrO7 and Sm2K2IrO7. The monoclinic crystal structure (space group C2/m, No.12) is stable down to 90 K and contains layers of IrO6 octahedra separated by Ba and AlO4 tetrahedra. The material exhibits insulating behavior with a narrow band gap of ∼0.6 eV. The positive Seebeck coefficient indicates hole-like dominant charge carriers. Susceptibility measurement shows antiferromagnetic coupling with no order down to 2 K.


Physical Review B | 2017

Non-uniform carrier density in Cd

Iris Crassee; E. Martino; C. C. Homes; Ondřej Caha; Jiří Novák; P. Tueckmantel; M. Hakl; A. Nateprov; E. Arushanov; Quinn Gibson; R. J. Cava; K. E. Arpino; T. M. McQueen; M. Orlita; Ana Akrap

We report the detailed optical properties of Cd


Physical Review B | 2017

_3

I. Crassee; F. Borondics; M. K. Tran; G. Autès; Arnaud Magrez; Ph. Bugnon; H. Berger; J. Teyssier; Oleg V. Yazyev; M. Orlita; Ana Akrap

_3


Journal of the Physical Society of Japan | 2008

As

Mirta Herak; Marko Miljak; Ana Akrap; László Forró; Helmuth Berger

As

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Dive into the Ana Akrap's collaboration.

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C. C. Homes

Brookhaven National Laboratory

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László Forró

École Polytechnique Fédérale de Lausanne

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G. D. Gu

Brookhaven National Laboratory

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Helmuth Berger

École Polytechnique Fédérale de Lausanne

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Jinsheng Wen

Brookhaven National Laboratory

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Zhiwei Lin

Brookhaven National Laboratory

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