Chiral Charge-Density Waves

Ishioka, Junya; Liu, Y. H.; Shimatake, K.; Kurosawa, T.; Ichimura, Kunihiro; Toda, Yasunori; Oda, Masahiro; Tanda, Satoshi

doi:10.1103/physrevlett.105.176401

Cited by 144 publications

(182 citation statements)

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“…The independence of the 1Q and 3Q Fourier components on Cu concentration and the marked electronhole asymmetry of the CDW gap exclude a Fermi surface nesting mechanism to explain the CDW. Figure 3 further questions the chiral nature of the CDW in 1T-TiSe 2 claimed in several STM studies [32,38] based on a systematic hierarchy in the amplitudes of the q 3Q CDW Fourier components. There is no supporting evidence for a chiral CDW in our images.…”

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confidence: 99%

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

et al. 2017

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“…We observed chiral CDWs as reported in our previous paper. 5 We found triangular FOs as denoted by the white and black solid circles [ Fig. 1(a)].…”

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“…The background chiral CDW shows the clockwise phase. 5 The interpretation of the FT image in real space is shown in Fig. 1(c).…”

Section: Resultsmentioning

confidence: 99%

“…5. By in situ cleavage method in the specimen chamber at 77 K and 10 −8 Pa, we obtained an atomically defect-free Se surface.…”

Section: Methodsmentioning

confidence: 99%

“…We have discovered chiral charge-density waves (CDWs) in 1T-TiSe 2 , 5 in which the macroscopic quantum state exhibits helicity in a static structure. If a charged impurity is added to an electron system, the Friedel oscillation for screening is induced.…”

Section: Introductionmentioning

confidence: 99%

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Charge-parity symmetry observed through Friedel oscillations in chiral charge-density waves

et al. 2011

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We discovered a chiral behavior of Friedel oscillations (FOs), which have both triangular symmetry and inverse chirality from chiral charge-density waves (CDWs) in 1T-TiSe 2 by using scanning tunneling microscopy (STM). Surprisingly, the existence of FOs with the opposite chirality to the underlying CDWs suggests that the excess electron induced by impurity reduces the local helicity of CDWs without CDW breaking. This FOs can be explained with a two-branch model with different chiralities, which permits excitation from one branch to another, that is, Dirac-type dispersion. Moreover, we found two states that correspond to electron addition and electron removal. In terms of the chirality of electrons, these two states are the same. This result provides an evidence for the charge-parity (CP) symmetry conservation in CDW systems.

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