Turgut Yilmaz

Turgut Yilmaz
Brookhaven National Laboratory · National Synchrotron Light Source II

PhD

About

65
Publications
10,799
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906
Citations
Additional affiliations
January 2018 - present
University of Connecticut
Position
  • PostDoc Position
September 2009 - August 2016
University of Connecticut
Position
  • PhD
September 2009 - August 2016
University of Connecticut
Position
  • PhD Student

Publications

Publications (65)
Preprint
Full-text available
Dispersionless flat bands are proposed to be a fundamental ingredient to achieve the various sought after quantum states of matter including high-temperature superconductivity 1-4 and fractional quantum Hall effect 5-6. Materials with such peculiar electronic states, however, are very rare and often exhibit very complex band structures. Here, we re...
Article
Full-text available
Here, by using angle-resolved photoemission spectroscopy, we showed that Bi2−xCrxSe3 single crystals have a distinctly well-defined band structure with a large bulk band gap and undistorted topological surface states. These spectral features are unlike their thin film forms in which a large nonmagnetic gap with a distorted band structure was report...
Article
Full-text available
Periodic lattice distortion, known as the charge density wave, is generally attributed to electron–phonon coupling. This correlation is expected to induce a pseudogap at the Fermi level in order to gain the required energy for stable lattice distortion. The transition metal dichalcogenide 1T-VSe2 also undergoes such a transition at 110 K. Here, we...
Preprint
Full-text available
Renew interest in the charge density wave phase of TiSe$_2$ stems from the realization of its unique driving mechanism, the so called excitonic insulator phase. Existing claims are motivated by model calculations of the band structure. In this study, angle resolved photoemsision spectroscopy and density functional theory for TiSe$_2$ are directly c...
Preprint
Full-text available
The electronic origin of the structural transition in 1T-VSe$_2$ is re-evaluated through an extensive angle-resolved photoemission spectroscopy experiment. The components of the band structure, missing in previous reports, are revealed. Earlier observations, shown to be temperature independent and therefore not correlated with the phase transition,...
Preprint
Full-text available
Kagome vanadates {\it A}V$_3$Sb$_5$ display unusual low-temperature electronic properties including charge density waves (CDW), whose microscopic origin remains unsettled. Recently, CDW order has been discovered in a new material ScV$_6$Sn$_6$, providing an opportunity to explore whether the onset of CDW leads to unusual electronic properties. Here...
Article
Full-text available
Kagome vanadates AV3Sb5 display unusual low-temperature electronic properties including charge density waves (CDW), whose microscopic origin remains unsettled. Recently, CDW order has been discovered in a new material ScV6Sn6, providing an opportunity to explore whether the onset of CDW leads to unusual electronic properties. Here, we study this qu...
Article
Two-dimensional electron gas (2DEG) states at oxide interfaces between two ferroic materials have been fertile ground to realize controllable multiferroicity. Here, we investigate the 2DEG states at the interface of ferroelectric BaTiO3 and a magnetic layer of iron using angle-resolved photoemission spectroscopy. Orbital-selective charge transfer o...
Article
Full-text available
Non-volatile phase-change memory devices utilize local heating to toggle between crystalline and amorphous states with distinct electrical properties. Expanding on this kind of switching to two topologically distinct phases requires controlled non-volatile switching between two crystalline phases with distinct symmetries. Here, we report the observ...
Article
Magnetism in two-dimensional (2D) materials has attracted considerable attention recently for both fundamental understanding of magnetism and its tunability towards device applications. The isostructural Fe3GeTe2 and Fe3GaTe2 are two members of the Fe-based van der Waals (vdW) ferromagnet family, but exhibit very different Curie temperatures (TC) o...
Article
Heterostructures of the topological insulator Bi2Se3 on transition metal dichalcogenides (TMDCs) offer a new materials platform for studying novel quantum states by exploiting the interplay among topological orders, charge orders, and magnetic orders. The diverse interface attributes, such as the material combination, charge rearrangement, defects,...
Article
Kagome metals with charge density wave (CDW) order exhibit a broad spectrum of intriguing quantum phenomena. The recent discovery of the novel kagome CDW compound ScV6Sn6 has spurred significant interest. However, understanding the interplay between CDW and the bulk electronic structure has been obscured by a profusion of surface states and termina...
Article
Full-text available
Electronic correlation effects are manifested in quantum materials when either the on-site Coulomb repulsion is large or the electron kinetic energy is small. The former is the dominant effect in cuprate superconductors and heavy-fermion systems whereas it is the latter in twisted bilayer graphene and geometrically frustrated metals. However, the s...
Article
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Heavy-fermion metals are prototype systems for observing emergent quantum phases driven by electronic interactions1–6. A long-standing aspiration is the dimensional reduction of these materials to exert control over their quantum phases7–11, which remains a significant challenge because traditional intermetallic heavy-fermion compounds have three-d...
Article
Superconductivity in topological insulators is expected to show very unconventional features such as a p+ip order parameter, Majorana fermions, etc. However, intrinsic superconductivity has been observed in a very limited number of materials in which the pairing symmetry is still a matter of debate. Here, we study the topological crystalline insula...
Article
Full-text available
The intertwining between spin, charge, and lattice degrees of freedom can give rise to unusual macroscopic quantum states, including high-temperature superconductivity and quantum anomalous Hall effects. Recently, a charge density wave (CDW) has been observed in the kagome antiferromagnet FeGe, indicative of possible intertwining physics. An outsta...
Article
Low temperature, high resolution angle resolved photoemission experiments performed on bulk 1T−TiSe2 samples display conspicuous band folding as the only prominent signature of the periodic lattice distortion. The presence of a bulk electronic gap supporting a charge density wave phase is not confirmed in light of the new data. These observations c...
Preprint
Full-text available
The ability to reversibly toggle between two distinct states in a non-volatile method is important for information storage applications. Such devices have been realized for phase-change materials, which utilizes local heating methods to toggle between a crystalline and an amorphous state with distinct electrical properties. To expand such kind of s...
Preprint
Full-text available
Magnetism in two-dimensional (2D) materials has attracted considerable attention recently for both fundamental understanding of magnetism and their tunability towards device applications. The isostructural Fe$_3$GeTe$_2$ and Fe$_3$GaTe$_2$ are two members of the Fe-based van der Waals (vdW) ferromagnet family, but exhibit very different Curie tempe...
Article
Full-text available
Transition metal dichalcogenides exhibit many fascinating properties including superconductivity, magnetic orders, and charge density wave. The combination of these features with a non-trivial band topology opens the possibility of additional exotic states such as Majorana fermions and quantum anomalous Hall effect. Here, we report on photon-energy...
Article
Full-text available
Understanding the interplay between magnetic and electronic degrees of freedom is of profound recent interest in different Eu-based magnetic topological materials. In this paper, we studied the magnetic and electronic properties of the layered Zintl-phase compound EuAl2Ge2 crystallizing in the trigonal CaAl2Si2-type structure. We report zero-field...
Article
Angle-resolved photoemission spectroscopy experiments reveal a surprisingly richer surface electronic structure in 1T−VSe2 than previously predicted or probed. Earlier claims supporting a charge density wave phase in this material are reexamined in terms of these findings and are found to be untenable. The Fermi surface is found to be gapless, whil...
Preprint
Full-text available
The magnetic and electronic properties of the layered Zintl-phase compound EuAl$_2$Ge$_2$ crystallizing in the trigonal CaAl$_2$Si$_2$-type structure are reported. Our neutron-diffraction measurements show that EuAl$_2$Ge$_2$ undergoes A-type antiferromagnetic (AFM) ordering below $T_{\rm N} = 27.5(5)$~K, with the Eu moments (Eu$^{2+}$, $S = 7/2$)...
Article
Dirac semimetals show nontrivial physical properties and can host exotic quantum states like Weyl semimetals and topological insulators under suitable external conditions. Here, by combining angle-resolved photoemission spectroscopy measurements (ARPES) and first-principle calculations, we demonstrate that the Zintl-phase compound SmMg2Bi2 is in cl...
Article
Full-text available
Topological semimetals are a frontier of quantum materials. In multiband electronic systems, topological band crossings can form closed curves, known as nodal lines. In the presence of spin–orbit coupling and/or symmetry-breaking operations, topological nodal lines can break into Dirac/Weyl nodes and give rise to interesting transport properties, s...
Preprint
Full-text available
The intricate interplay between spin, charge, and lattice degrees of freedom is the key for macroscopic quantum states, including high-temperature superconductivity and quantum anomalous Hall effects. Recently, significant interests have been focused on the kagome superconductor AV$_3$Sb$_5$ (A=K, Rb, Cs), where van Hove singularities near the Ferm...
Preprint
Full-text available
Dirac semimetals show nontrivial physical properties and can host exotic quantum states like Weyl semimetals and topological insulators under suitable external conditions. Here, by combining angle-resolved photoemission spectroscopy measurements (ARPES) and first-principle calculations, we demonstrate that Zintl-phase compound SmMg2Bi2 belongs to t...
Preprint
Full-text available
Here, our angle resolved photoemission spectroscopy experiment reveled that the surface band structure of the 1T-VSe2 host electronic states that was not predicted or probed before. Earlier claims to support charge density wave phase can be all explained in terms of these new findings. Its Fermi surface found to be not gaped at any point of the Bri...
Article
As a two-dimensional structural motif, the kagome net produces many interesting magnetic and electronic properties. In particular, this lattice produces flat electronic bands with a large density of states. When the chemical potential is positioned within these flat bands, electronic instabilities can result. For the kagome metal CoSn, this alignme...
Article
We present detailed high-resolution angle-resolved photoemission experiments on VSe2 grown under various conditions. The surface electronic structure optimally grown samples can host high-temperature spectral kink, quasiparticle peak, and the Fermi gap. Collective observation of these electronic features refers to the strong electronic correlation...
Preprint
Full-text available
Destructive interference of electron hopping on the frustrated kagome lattice generates Dirac nodes, saddle points, and flat bands in the electronic structure. The latter provides the narrow bands and a peak in the density of states that can generate correlated electron behavior when the Fermi level lies within them. In the kagome metal CoSn, this...
Preprint
Topological semimetals are a frontier of quantum materials. In multi-band electronic systems, topological band-crossings can form closed curves, known as nodal lines. In the presence of spin-orbit coupling and/or symmetry-breaking operations, topological nodal lines can break into Dirac/Weyl nodes and give rise to novel transport properties, such a...
Preprint
Full-text available
Controlling the density of electrons inside an insulator via the chemical potential is a cornerstone of modern electronics, enabling the electrical conductivity of semiconductors and the emergence of fascinating new properties linked with electronic correlations. The compound SmB 6 has drawn widespread attention in recent years as the first insulat...
Article
Here, we study the surface electronic structure of 1T−VSe2 by means of angle-resolved photoemission spectroscopy and uncover a dispersionless emission located in the vicinity of the Fermi level. Its crystal momentum dependency reveals that it occupies large portions of the Brillouin zone, where no bulk band is expected. Upon electron doping (deposi...
Preprint
Full-text available
High-resolution angle-resolved photoemission experiments reveal subtle modifications of the surface electronic structure of VSe2. Most remarkably, we show that superconductivity can be induced in VSe2 by the right selection of substrate and growth parameters. Evidence for the superconducting state comes from the simultaneous detection of spectral k...
Preprint
Full-text available
Here, we study the surface electronic structure of 1T-VSe2 by means of angle resolved photoemission spectroscopy and uncover a dispersion-less emission located in the vicinity of the Fermi level. Its crystal momentum dependency reveals that it occupies large portions of the Brillouin zone (BZ), where no bulk band is expected. Upon electron doping (...
Article
SmB6 is a strongly correlated material that has been attributed as a topological insulator and a Kondo insulator. Recent studies have found the topological surface states and low temperature insulating character to be profoundly robust against magnetic and nonmagnetic impurities. Here, we use angle resolved photoemission spectroscopy to chart the e...
Article
Full-text available
The combination of nontrivial band topology and symmetry-breaking phases gives rise to novel quantum states and phenomena such as topological superconductivity, quantum anomalous Hall effect, and axion electrodynamics. Evidence of intertwined charge density wave (CDW) and superconducting order parameters has recently been observed in a novel kagome...
Preprint
Full-text available
SmB6 is a strongly correlated material that has been attributed as a topological insulator and a Kondo insulator. Recent studies have found the topological surface states and low temperature insulating character to be profoundly robust against magnetic and non-magnetic impurities. Here, we use angle resolved photoemission spectroscopy to chart the...
Preprint
Full-text available
Electronic flat band systems are a fertile platform to host correlation-induced quantum phenomena such as unconventional superconductivity, magnetism and topological orders. While flat band has been established in geometrically frustrated structures, such as the kagome lattice, flat band-induced correlation effects especially in those multi-orbital...
Article
Samarium hexaboride is a candidate for the topological Kondo insulator state, in which Kondo coherence is predicted to give rise to an insulating gap spanned by topological surface states. Here we investigate the surface and bulk electronic properties of magnetically alloyed Sm1−xMxB6 (M=Ce, Eu), using angle-resolved photoemission spectroscopy and...
Article
Full-text available
In the present work, we investigate the electronic structure of the two-dimensional ferromagnet Cr 2 Ge 2 Te 6 by photoemission spectroscopy and ab initio calculations. Our results demonstrate the presence of multi-hole–type bands in the vicinity of the Fermi level indicating that the material can support high electrical conductivity by manipulatin...
Preprint
Full-text available
The combination of non-trivial band topology and symmetry breaking phases gives rise to novel quantum states and phenomena such as topological superconductivity, quantum anomalous Hall effect and axion electrodynamics. Evidence of intertwined charge density wave (CDW) and superconducting order parameters has recently been observed in a novel kagome...
Article
Full-text available
Flat band electronic states are proposed to be a fundamental tool to achieve various quantum states of matter at higher temperatures due to the enhanced electronic correlations. However, materials with such peculiar electronic states are rare and often rely on subtle properties of the band structures. Here, by using angle-resolved photoemission spe...
Article
Full-text available
Flat band electronic states are proposed to be a fundamental tool to achieve various quantum states of matter at higher temperatures due to the enhanced electronic correlations. However , materials with such peculiar electronic states are rare and often rely on subtle properties of the band structures. Here, by using angle-resolved photoemission sp...
Preprint
Full-text available
In the present work, we investigate the electronic structure of the two-dimensional (2D) ferromagnet Cr2Ge2Te6 by photoemission spectroscopy and ab initio calculations. Our results demonstrate the presence of multiple hole-type bands in the vicinity of the Fermi level indicating that the material can support high electrical conductivity by manipula...
Article
In this article, we report a comparative study of the electronic structure of Cr-doped and pristine Bi2Se3. Circular dichroism and photon-energy-dependent angle-resolved photoemission experiments were performed. Even though the surface states seen on the Cr-doped samples are gapped, they exhibit strong circular dichroism, for which we provide its o...
Preprint
Full-text available
The unconventional normal-state properties of the cuprates are often discussed in terms of emergent electronic order that onsets below a putative critical doping, xc=0.19. Charge density wave (CDW) correlations represent one such order; however, experimental evidence for such order generally spans a limited range of doping that falls short of the c...
Article
Full-text available
Non-magnetic gap at the Dirac point of topological insulators remains an open question in the field. Here, we present angle-resolved photoemission spectroscopy experiments performed on Cr-doped Bi2Se3 and showed that the Dirac point is progressively buried by the bulk bands and a low spectral weight region in the vicinity of the Dirac point appears...
Article
Full-text available
Correction for ‘Origin of the temperature dependence of the energy gap in Cr-doped Bi 2 Se 3 ’ by Turgut Yilmaz et al. , Phys. Chem. Chem. Phys. , 2018, DOI: 10.1039/c7cp08049b.
Article
Full-text available
In this report, we identify the origin of the temperature dependence of the surface energy gap in impurity-doped topological insulators. The gap at the Dirac point and its variation with temperature were studied by using angle-resolved photoemission spectroscopy in Cr-doped Bi2Se3. Our valence band photoemission results revealed that the gap varies...
Preprint
Full-text available
In this report, we identify the origin of the temperature dependence of the surface energy gap in impurity-doped topological insulators. The gap at the Dirac point and its variation with temperature were studied by using angle-resolved photoemission spectroscopy in Cr-doped Bi2Se3. Our valence band photoemission results revealed that the gap varies...
Article
Full-text available
In this report, we demonstrate that the energy gap in Cr-doped Bi2Se3 closes and reopens in oscillatory fashion with increasing sample thickness indicating the topological quantum phase transition driven by the quantum finite size effect. The pattern of the oscillation provides an evidence that Cr-doped Bi2Se3 can have a Dirac semimetal state depen...
Conference Paper
Full-text available
Reducing the radar cross section (RCS) of potential targets (aircrafts, ground-based vehicles) has been a problem of longstanding interest. There exist two different approaches to create this desired "low observability": (i) reducing the RCS via target shaping that minimizes the backscatter and (ii) using radar absorbing materials (RAMs) that cover...
Article
Full-text available
In this report, it is shown that Cr doped into the bulk and Cr deposited on the surface of Bi2Se3 films produced by molecular beam epitaxy (MBE) have strikingly different effects on both the electronic structure and chemical environment. Angle resolved photoemission spectroscopy (ARPES) shows that Cr doped into the bulk opens a surface state energy...
Article
Full-text available
Magnetic and dielectric materials can be blended to enhance absorption properties at microwave frequencies, although the materials may have relatively weak attenuation capabilities by themselves. The specific goal of this work is to enhance microwave absorption properties of materials with interesting dielectric behavior by blending them with magne...
Article
Ph.D. Dissertation Turgut Yilmaz Graduate Student UConn Department of Physics "Photoemission Studies of Topological Insulators" Topological insulators (TIs) attracted scientist due to its distinct electronic structure. TIs possess metallic surfaces due to strong spin orbit coupling, while the bulk shows the insulating behavior. On the surface of TI...
Article
Full-text available
A systematic investigation of the thickness and oxygen pressure dependence for the structural properties of ultra-thin epitaxial magnetite (Fe3O4) films has been carried out; for such films, the structural properties generally differ from those for the bulk when the thickness ⩽10 nm. Iron oxide ultra-thin films with thicknesses varying from 3 nm to...
Article
Full-text available
The performance of spintronic devices depends critically on the ability to control the properties of high spin-polarization materials such as magnetite (Fe3O4) in thin films. In this work, the effect of oxygen pressure on the transport and magnetic properties of Fe3O4 thin films was extensively investigated. The 20 nm Fe3O4 films were grown on MgO...
Article
Full-text available
Three-dimensional topological insulators and topological crystalline insulators represent new quantum states of matter, which are predicted to have insulating bulk states and spin-momentum-locked gapless surface states. Experimentally, it has proven difficult to achieve the high bulk resistivity that would allow surface states to dominate the trans...
Article
Proximity-induced superconductivity in a 3D topological insulator represents a new avenue for observing zero-energy Majorana fermions inside vortex cores. Relatively small gaps and low transition temperatures of conventional s-wave superconductors put hard constraints on these experiments. Significantly larger gaps and higher transition temperature...
Article
Full-text available
Proximity-induced superconductivity in a 3D topological insulator represents a new avenue for observing zero-energy Majorana fermions inside vortex cores. Relatively small gaps and low transition temperatures of conventional s-wave superconductors put the hard constraints on these experiments. Significantly larger gaps and higher transition tempera...

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