Charge ordering and disordering transitions in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Pr</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mi>−</mml:mi><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Ca</mml:mi></mml:mrow><mml:mrow><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">MnO</mml:mi>

Okimoto, Y.; Tomioka, Y.; Onose, Y.; Otsuka, Yuichi; Tokura, Y.

doi:10.1103/physrevb.57.r9377

Cited by 118 publications

(64 citation statements)

References 18 publications

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“…The T variation of the absorption coefficient of this material is negligible at the center of the laserwavelength used in the photoexcitation. [19] We found that E THz tends to decrease as T is increased around 120 K. For further increase with T , E THz monotonically increases up to 230 K. Even at the room T , the THz radiation is clearly observed. These critical points matches with previously reported values; T CA , T N , and T CO/OO .…”

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confidence: 74%

“…The energy of the optical pulse exceeds the charge-gap energy ∼0.5 eV of PCMO and nearly corresponds to the charge transfer energy from O 2p to Mn 3d band. [19] The pump-pulses chopped mechanically at 2 kHz were focused into the region of 30 µm in diameter by an object lens on the gap of the bow-tie antenna. In order to enhance the collection efficiency of the THz-pulse, we attached an MgO hemispherical lens on the backside of the MgO substrate.…”

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confidence: 99%

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Terahertz radiation from magnetoresistive Pr0.7Ca0.3MnO3 thin films

Kida

Tonouchi

2001

Applied Physics Letters

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Terahertz (THz) radiation with its spectrum extending up to 1 THz has been observed by an illumination of femtosecond optical pulses to optical switching devices fabricated on magnetoresistive manganite thin films; Pr0.7Ca0.3MnO3. The THz radiation strongly depends on temperature T and its T trend reverses sign across charge-orbital and spin ordering T 's.PACS numbers: 75.30.Vn (Colossal magnetoresistance), 42.65.Re (Ultrafast processes; optical pulse generation and pulse compression), 07.57.Hm (Infrared, submillimeter wave, microwave, and radiowave sources)The progress of a THz-pulse generation and detection system using the photoconductive switch excited by femtosecond optical pulses, [1] caused to general appreciations of this phenomenon and it rapidly gained ground as a result of many subsequent experimental and theoretical efforts.[2] The studies are oriented toward to the discovery of the THz radiation from various kind of materials including semiconductors, quantum wells, and superconductors. [2,3,4,5] The basic mechanism of the THz radiation from these materials can be understood in the following classical Maxwell's equation, [2]where E is the radiation field at the far-field and J the current. In other words, the transient current, typically of the order of subpicosecond, is created by exciting carriers with ultrafast optical pulses, which in turn produce the THz-pulse propagating into the free space based on Eq.(1). This manifests itself as the optical conversion via the transient photocurrent by the optical pulses.In this letter, we show the finding of the THz radiation from magnetoresistive manganites and also describe how its characteristics vary with external stimulations. To the best of our knowledge, the THz radiation from magnetic materials has not been observed so far.Hole-doped manganites with a perovskite structure, especially Pr 0.7 Ca 0.3 MnO 3 (PCMO) investigated here, has attracted great interests not only because of their potential applications to colossal magnetoresistive (CMR) devices but also their following unique features.[6] It exhibits insulating behavior with temperature T ; charge and orbital ordering (a checkerboard pattern of Mn 3+ and Mn 4+ ions with 1:1 ratio) occur at T CO/OO and CE-type antiferromagnetic ordering develops below T N . Below T CA , it transforms to the charge-orbital ordered spin-canted antiferromagnetic insulator. [7] This phase can be easily melted to the charge-orbital disordered ferromagnetic metallic state by external perturbations such * Electronic address: kida@rcsuper.osaka-u.ac.jp as magnetic field (CMR effect), [7] (1), it is expected that the THz-pulse can also be generated from PCMO, however its mechanism is basically different from semiconductors and the ultrafast optical modulation of the charge, spin, and orbital ordering may be responsible for this effect. In this purpose, we found the THz radiation from PCMO thin films excited by femtosecond optical pulses.PCMO thin films on MgO(100) substrates were prepared by pulsed laser deposition techni...

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Terahertz radiation from magnetoresistive Pr0.7Ca0.3MnO3 thin films

Kida

Tonouchi

2001

Applied Physics Letters

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“…Another explanation is that the charge gap is affected by the electron-electron interaction. Such a correlationdriven enhancement of the gap is though to be present in several manganites like Bi 1−x Ca x MnO 3 (x = 0.74−0.82) [14], Pr 0.6 Ca 0 .4MnO 3 [15] and La 1−x Ca x MnO 3 (x ≥ 0.6) and in the nickelate NdNiO 3 [16] where the gap parameter is ∼ 20, ∼ 9, ∼ 10 and ∼ 20, respectively. The temperature dependence of the gap in all of the above cited 3d compounds fairly follows the BCS functional form while in BaVS 3 the transition appears in ∆ ch in a much sharper manner.…”

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Pressure-induced suppression of the spin-gapped insulator phase inBaVS3: An infrared optical study

et al. 2005

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The metal-insulator (MI) transition in BaVS3 has been studied at ambient pressure and under hydrostatic pressure up to p = 26 kbar in the frequency range of 20 − 3000 cm −1 . The charge gap determined from the optical reflectivity is enhanced, ∆ ch (p)/kBTMI (p) ∼ 12. This ratio is independent of pressure indicating that the character of the transition does not vary along the p − T phase boundary. Above the critical pressure, pcr ∼ 20 kbar, metallic spectra were recorded in the whole temperature range, as expected from the shape of the phase diagram. Our results exclude the opening of a pseudogap above TMI at any pressure. Below TMI an unusually strong temperature dependence of the charge gap was observed, resulting in a ∆ ch (T ) deviating strongly from the mean field-like variation of the structural order parameter.A class of symmetry breaking phase transitions, characterized by an anomalously large gap parameter, has recently attracted much attention and has been investigated intensely in the wider framework of strongly correlated electron systems. Though in some manganites and nickelates the huge enhancement of the ∆/k B T c ratio, sometimes as large as ∼ 30, is accompanied by the opening of a pseudogap above T c [1, 2], in most cases a mean-field-like temperature dependence of ∆ is observed. In contrast, in first order metal-insulator transitions a more drastic, often discontinuous opening of the charge gap is seen. On the other hand, the transition in the inorganic spin-Peierls system CuGeO 3 looks almost like a first order one, as the opening of the singlet-triplet gap is much sharper than the BCS functional form and follows ∆ ∝ (T c − T ) β with β ≈ 0.1 instead of 0.5 [3]. In BaVS 3 , the detailed temperature dependence of neither the spin gap nor the charge gap has been measured so far. The present study of the infrared (IR) optical properties demonstrates that electron correlations play crucial role in BaVS 3 : they lead to a large enhancement of the ∆/k B T c ratio and simultaneously give rise to an abrupt temperature dependence of ∆.At ambient pressure BaVS 3 exhibits a phase transition from a high-temperature paramagnetic "bad metal" phase to a low-temperature singlet insulator state at. This is a second order phase transition, as it has been pointed out recently by the comparison of the anomalies observed in different thermodynamic properties [5]. The observation of the crystal symmetry lowering [6] in more recent X-ray experiments provided direct evidence for the second order character of the transition at T MI ≈ 70 K.The metallic nature of the compound is enhanced by the application of hydrostatic pressure and the transition temperature is suppressed at an average rate of ∆T MI /∆p ≈ 3.4 K/kbar [7,8]. The critical pressure above which the metallic phase extends over the whole temperature range is p cr ≈ 20 kbar [8]. The suppression of the insulating phase is accompanied by a monotonic decrease of the spin gap [5]. Moreover, the phenomenon occurring at T MI ≈ 70 K at ambient pressure has been desc...

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“…In LCMO/BFO, the induced AFM order at the interface will increase θ ij in LCMO [Fig 3(a)], suppressing in-plane electron hopping. This results in a discernible difference between LCMO and LCMO/BFO in a high B field, which increases the alignment of the induced AFM spins [38,39] while keeping the ordered FM spins saturated. We note that neutron diffraction measurements on LSMO/BFO superlattices grown in the same system at LANL have revealed a reduced magnetization in the LSMO layers, supporting this hypothesis [48].…”

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confidence: 99%

“…The applied field enhances the spin alignment, increasing the conductivity, which reduces the polaronic peak and recovers the Drude-like feature [i.e., following the blue solid line from the lower to the upper panel in Fig. 1(b)] [25,[36][37][38][39][40][41].…”

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Polaronic Transport Induced by Competing Interfacial Magnetic Order in aLa0.7Ca0.3MnO3/BiFe

Sheu

Trugman

et al. 2014

Phys. Rev. X

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Using ultrafast optical spectroscopy, we show that polaronic behavior associated with interfacial antiferromagnetic order is likely the origin of tunable magnetotransport upon switching the ferroelectric polarity in a La 0.7 Ca 0.3 MnO 3 =BiFeO 3 (LCMO/BFO) heterostructure. This is revealed through the difference in dynamic spectral weight transfer between LCMO and LCMO/BFO at low temperatures, which indicates that transport in LCMO/BFO is polaronic in nature. This polaronic feature in LCMO/BFO decreases in relatively high magnetic fields due to the increased spin alignment, while no discernible change is found in the LCMO film at low temperatures. These results thus shed new light on the intrinsic mechanisms governing magnetoelectric coupling in this heterostructure, potentially offering a new route to enhancing multiferroic functionality. The quest to achieve strong magnetoelectric coupling has driven the surge in research on multiferroic materials over the past decade. However, this has been quite difficult to accomplish using bulk materials, motivating researchers to explore other approaches, most notably the use of transition metal oxide heterostructures [1][2][3]. In these novel systems, different degrees of freedom (DOFs) (e.g., charge, spin, and orbital) are coupled at a single interface between two different oxide layers to form a new state that displays properties dramatically different from those of the individual layers [4][5][6][7][8]. Particular attention has been given to the coupling between ferromagnetic (FM), antiferromagnetic (AFM), and ferroelectric (FE) orders, as this could reveal new routes to realizing strong magnetoelectric coupling [1][2][3][9][10][11].Heterostructures consisting of manganite and multiferroic layers are particularly promising in this regard. The most extensively studied combination [2,3,9,10,12] consists of the colossal magnetoresistive manganite La 0.7 Sr 0.3 MnO 3 (LSMO) [or the similar compound La 0.7 Ca 0.3 MnO 3 (LCMO)], which is ferromagnetic below a critical temperature T c , and the canonical multiferroic BiFeO 3 (BFO), which has coexisting coupled AFM and FE phases in which the magnetization can be switched by an applied electric (E) field [13]. The combination of these materials thus has great potential for exhibiting novel phenomena by coupling different FM, AFM, and FE phases across the interface. Indeed, a new interfacial state between LSMO and BFO has been discovered experimentally and discussed theoretically [2,[14][15][16]. This state displays an exchange-bias field and magnetotransport that can be tuned by switching the FE polarization, increasing the potential for device control through interfacial coupling. However, a complete picture of the interplay between FM and AFM orders in this heterostructure has yet to be reached.Current understanding of the exchange-bias field, which arises from the interaction between FM and G-type AFM [AFMðGÞ] orders at the interface, is based on spin canting or pinning in BFO, with the assumption of negligible canting in ...

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Charge ordering and disordering transitions inPr1−xCaxMnO

Cited by 118 publications

References 18 publications

Terahertz radiation from magnetoresistive Pr0.7Ca0.3MnO3 thin films

Terahertz radiation from magnetoresistive Pr0.7Ca0.3MnO3 thin films

Pressure-induced suppression of the spin-gapped insulator phase inBaVS3: An infrared optical study

Polaronic Transport Induced by Competing Interfacial Magnetic Order in aLa0.7Ca0.3MnO3/BiFe

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