Emergence of Fermi Pockets in a New Excitonic Charge-Density-Wave Melted Superconductor

Qian, Dong; Hsieh, David; Wray, L. Andrew; Morosan, Emilia; Wang, N. L.; Xia, Y.; Cava, R. J.; Hasan, M. Zahid

doi:10.1103/physrevlett.98.117007

Cited by 112 publications

(78 citation statements)

References 32 publications

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“…In particular, we confirm Cu is a donor contributing delocalized electrons at the Fermi level and shifting the chemical potential up in energy in agreement with previous ARPES results [19,20]. We observe a striking instability towards the formation of charge stripes at low Cu concentration (x < 0.02) and the formation of short-range ordered domains which tend to be phase shifted at higher Cu contents (x > 0.05).…”

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confidence: 91%

Stripe and Short Range Order in the Charge Density Wave of 1T−CuxTiSe2

et al. 2017

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We study the impact of Cu intercalation on the charge density wave (CDW) in 1T-Cu x TiSe 2 by scanning tunneling microscopy and spectroscopy. Cu atoms, identified through density functional theory modeling, are found to intercalate randomly on the octahedral site in the van der Waals gap and to dope delocalized electrons near the Fermi level. While the CDW modulation period does not depend on Cu content, we observe the formation of charge stripe domains at low Cu content (x < 0.02) and a breaking up of the commensurate order into 2 × 2 domains at higher Cu content. The latter shrink with increasing Cu concentration and tend to be phase shifted. These findings invalidate a proposed excitonic pairing as the primary CDW formation mechanism in this material. DOI: 10.1103/PhysRevLett.118.017002 Correlated electron systems are prone to develop distinct electronic ground states, such as superconductivity, charge density waves (CDWs), and spin ordered phases. The nature of the interplay between these ground states is the focus of intense research efforts. A CDW is a spatial modulation of the electron density associated with local lattice distortions. CDWs are found in a number of quasitwo-dimensional superconductors, including transition metal dichalcogenides [1], intercalated graphite [2], cuprates [3-5] and pnictides [6]. Of particular interest, largely driven by the puzzle of high temperature superconductivity, is whether charge order is competing, cooperating, or simply coexisting with superconductivity [7]. The layered transition metal dichalcogenide 1T-TiSe 2 offers an attractive playground to explore the interplay between these two electronic ground states, thus potentially contributing to resolving similar outstanding questions in cuprate superconductors and other strongly correlated materials.1T-TiSe 2 consists of a stack of van der Waals (vdW) coupled layers allowing in situ preparation of surfaces ideally suited for scanning probe investigations by cleaving. When cooled below T CDW ≃ 200 K, it undergoes a second-order phase transition into a commensurate 2 × 2 × 2 CDW superlattice [8,9]. There is currently no consensus on the origin of the CDW in this material. Two possible scenarios are being considered, one based on a purely electronic process characterized by an excitonic instability [8], while the other one involves a Jahn-Teller (JT) distortion [10]. More refined theories also propose a mixture of these two possible contributions, in the so called indirect JT transition [11][12][13].1T-TiSe 2 becomes superconducting when intercalating more than x ¼ 0.04 copper into the vdW gap, with a maximum critical temperature T c ¼ 4.1 K near x ¼ 0.08 [14]. Transport measurements [14,15] indicate the CDW is suppressed upon increasing the Cu content which would suggest a competition with superconductivity. A more recent report of an incommensurate CDW above the superconducting dome in pristine crystals under pressure [16] suggests a more complex scenario, where CDW fluctuations promote superconductivity. Traces of ...

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confidence: 91%

Stripe and Short Range Order in the Charge Density Wave of 1T−CuxTiSe2

et al. 2017

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“…[43] Intercalation with Cu atoms shifts the chemical potential of 1T-TiSe 2 by 0.1 eV. [53,54] Since the circumstances in the pristine material are nearly ideal for the formation of excitons, they deteriorate quickly upon intercalation, leaving a dominant role for the phonons in the CDW formation in this part of the phase diagram. As explained above, such a scenario naturally leads to a superconducting dome centered around the critical value of intercalation.…”

Section: Hybrid Phonon-exciton Modelmentioning

confidence: 99%

Superconductivity and hybrid soft modes inTiSe2

et al. 2016

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“…Photoemission studies have shown that the CDW order parameter microscopically competes with superconductivity in the same band. 3 In addition, previous work suggests that the CDW is suppressed by increasing the chemical potential, while superconductivity is enhanced by the increasing density of states (DOS).…”

Section: -5mentioning

confidence: 99%

Point-contact tunneling spectroscopy measurement ofCuxTiSe2: Disorder-enhanced Coulomb effects

Luna

Chen

et al. 2015

Phys. Rev. B

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We performed point-contact spectroscopy tunneling measurements on CuxTiSe2 bulk with x = 0.02 and 0.06 at temperatures ranging from T = 4 − 40 K and observe a suppression in the density of states around zero-bias that we attribute to enhanced Coulomb interactions due to disorder. We find that the correlation gap associated with this suppression is related to the zero-temperature resistivity. We use our results to estimate the disorder-free transition temperature and find that the clean limit Tc0 is close to the experimentally observed Tc.

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Emergence of Fermi Pockets in a New Excitonic Charge-Density-Wave Melted Superconductor

Cited by 112 publications

References 32 publications

Stripe and Short Range Order in the Charge Density Wave of 1T−CuxTiSe2

Stripe and Short Range Order in the Charge Density Wave of 1T−CuxTiSe2

Superconductivity and hybrid soft modes inTiSe2

Point-contact tunneling spectroscopy measurement ofCuxTiSe2: Disorder-enhanced Coulomb effects

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