Cohn Lab

Materials that possess layered or chain-like character in their crystal structures may harbor electron or lattice dynamical properties that behave as two-dimensional or one-dimensional. A tendency toward stronger electron interactions (via Coulombic or magnetic exchange forces) in lower dimensions can result in novel phase transitions (charge and spin density waves, unconventional superconductivity) or substantial heat conduction by magnetic excitations. The “correlated-electron” physics underlying these phenomena are topics of significant fundamental interest and can form the basis of new electronic or magnetic applications.

J. L. Cohn, C. A. M. dos Santos, and J. J. Neumeier, Superconductivity at carrier density 10¹⁷ cm⁻³ in quasi-one-dimensional Li_0.9Mo₆O₁₇, Physical Review B 108, L100512 (2023). 

D. S. Inosov, Y. O. Onykiienko, Y. V. Tymoshenko, A. Akopyan, D. Shukla, N. Prasai, M. Doerr, S. Zherlitsyn, D. Voneshen M. Boehm, V. Tsurkan, V. Felea, A. Loidl, and J. L. Cohn, Magnetic-field dependence of low-energy magnons, anisotropic heat conduction, and spontaneous relaxation of magnetic domains in the cubic helimagnet ZnCr₂Se₄, Physical Review B 102, 184431 (2020).

D. Shukla, N. Prasai, T. M. Carlino, M. M. A. Mazza, A. M. Scott, and J. L. Cohn, Anisotropic Heat Conduction in the Metal Organic Framework Perovskites [C(NH₂)₃]X(HCOO)₃ (X=Cu, Zn), Applied Physics Letters 114, 081907 (2019).

N. Prasai, A. Akopyan, B. A. Trump, G. G. Marcus, S. X. Huang, T. M. McQueen, and J. L. Cohn, Spin phases of the helimagnetic insulator Cu₂OSeO₃ probed by magnon heat conduction, Physical Review B 99, 020403(R) (2019).

N. Prasai, A. B. Christian, J. J. Neumeier, and J. L. Cohn, Resonant scattering of phonons in the quasi-one-dimensional spin-chain compounds AB₂O₆ (A = Ni, Co; B = Sb, Ta), Physical Review B 98, 134449 (2018).

N. Prasai, B. Trump, M. Marcus, A. Akopyan, S.-X. Huang, McQueen, and J. L. Cohn, Ballistic magnon heat conduction and possible Poiseuille flow in the helimagnetic insulator Cu₂OSeO₃. Physical Review B 95, 224407 (2017) (Editor’s Suggestion). 

S. Moshfeghyeganeh, A. N. Cote, J. J. Neumeier and J. L. Cohn, Anisotropic transport in the quasi-one-dimensional semiconductor Li_0.33MoO₃, Journal of Applied Physics 119, 095105 (2016).

S. H. Masunaga, A. Rebello, A. T. Schye, N.Prasai, J. J. Neumeier, and J. L. Cohn, Heat capacity, thermal expansion and heat transport in the Han Blue (BaCuSi₄O₁₀): Observation of structural phase transitions, Journal of Physics and Chemistry of Solids 85, 69 (2015).

N. Prasai, A. Rebello, A. B. Christian, J. J. Neumeier, and J. L. Cohn, Phonon-spin scattering and magnetic heat transport in the quasi-one-dimensional spin-1/2 antiferromagnetic chain compound CuSb₂O₆, Physical Review B 91, 054403 (2015). 

J. L.Cohn, B. D. White, C. A. M. dos Santos, and J. J. Neumeier, Giant Nernst Effect and Bipolarity in the Quasi-One-Dimensional Metal, Li_0.9Mo₆O₁₇, Physical Review Letters 108, 056604 (2012) (Editor’s Suggestion) Featured in Physics Synopsis. 

J. L. Cohn, P. Boynton, J. S. Triviño, J. Trastoy, B. D. White, C. A. M. dos Santos, and J. J. Neumeier, Stoichiometry, structure, and transport in the quasi-one- dimensional metal Li_0.9Mo₆O₁₇, Physical Review B 86, 195143 (2012).

A. de Campos, M. S. da Luz, C. A. M. dos Santos, A. T. Rice, A. M. Deml, B. D. White, J. J. Neumeier, and J. L. Cohn, Physical properties of quasi-one-dimensional SrNbO_3.41 and Luttinger liquid analysis of electrical transport, Physical Review B 82, 125117 (2010).

B. D. White, J. A. Souza, C. Chiorescu, J. J. Neumeier, and J. L. Cohn, Magnetic, transport, and thermodynamic properties of CaMn₂O₄ single crystals, Physical Review B 79, 104427 (2009).

Thin films and layered heterostructures (two or more layers in intimate contact) are the basis of many modern functional devices for information storage, sensing, signal processing, etc. For example, changing the thickness of thin layers deposited atop bulk crystalline surfaces may allow for controllably modulating the properties of the thin layers in novel ways that pave the way for new functionality and applications.

A. Akopyan, N. Prasai, B. A. Trump, G. G. Marcus, T. M. McQueen, and J. L. Cohn, Spin Seebeck Effect in Cu₂OSeO₃: Test of Bulk Magnon Spin-Current Theory, Physical Review B 101, 100407(R) (2020).

E. J. Moon, J. M. Rondinelli, N. Prasai, B. A. Gray, M. Kareev, J. Chakhalian, and J. L. Cohn, Strain-controlled band engineering and self-doping in ultrathin LaNiO₃ films, Physical Review B 85, 121106(R) (2012).

J. Chakhalian, J. M. Rondinelli, Jian Liu, B. A. Gray, M. Kareev, E. J. Moon, N. Prasai, J. L. Cohn, M. Varela, I. C. Tung, M. J. Bedzyk, S. G. Altendorf, F. Strigari, B. Dabrowski, L. H. Tjeng, P. J. Ryan, and J.W. Freeland, Asymmetric Orbital-Lattice Interactions in Ultrathin Correlated Oxide Films, Physical Review Letters 107, 116805 (2011).

K. Neupane, J. J. Neumeier, and J. L. Cohn, Anisotropic in-plane strain and transport in epitaxial Nd_0.2Sr_0.8MnO₃ thin films, Journal of Applied Physics 106, 123904 (2009).

J. L. Cohn, M. Peterca, and J. J. Neumeier, Giant dielectric permittivity of electron-doped manganite thin films, Ca_1-xLa_xMnO₃ (0<=x<=0.03), Journal of Applied Physics 97, 034102 (2005).

R. Maier and J. L. Cohn, Ferroelectric and ferrimagnetic iron-doped thin-film BaTiO3: Influence of iron on physical properties, Journal of Applied Physics 92, 5429 (2002).

R. Maier, J. L. Cohn, J. J. Neumeier, and L. A. Bendersky, Ferroelectricity and ferrimagnetism in iron-doped BaTiO₃, Applied Physics Letters 78, 2356 (2001).

L. A. Bendersky, R. Maier, J. L. Cohn, and J. J. Neumeier, Structural studies of pulsed-laser-deposited Ba₄Fe₄Ti₃O₁₆ oxide films, Journal of Materials Research 15, 1389 (2000).

Thermoelectric materials are those that exhibit large thermoelectric effects that can be harnessed for applications in power generation, electronic refrigeration, or energy sensing. Thermoelectric effects are phenomena by which a temperature difference generates an electric field or an electric current generates a temperature difference. The most important phenomena for applications are the Seebeck effect (a voltage induced by a temperature difference) and Peltier effect (driving heat flow with an electric current). All materials have nonzero thermoelectric effects, but for most they are too small to be useful. A low lattice thermal conductivity is an important ingredient for many thermoelectric applications. Doped semiconductors having open cavities in their structures into which loosely-bound guest atoms may be incorporated (skutterudites, clathrates) or those for which lattice scattering can be induced through nanostructuring, have been a focus of intense research for decades.

G.S. Nolas, J.L. Cohn, J. S. Dyck, C. Uher, G. A. Lamberton, Jr., and T.M. Tritt, Low temperature transport properties of polycrystalline Ba₈Ga₁₆Sn₃₀, Journal of Materials Research 19, 3556 (2004).

G. S. Nolas, D. G. Vanderveer, A. P. Wilkinson, and J. L. Cohn, Temperature dependent structural and transport properties of the type II clathrates A₈Na₁₆E₁₃₆ (A = Cs or Rb and E = Ge or Si), Journal of Applied Physics 91, 8970 (2002).

G. S. Nolas, J. L. Cohn, J. S. Dyck, C. Uher, and J. Yang Transport properties of polycrystalline type-I Sn clathrates, Physical Review B 65, 165201 (2002).

G. S. Nolas, T. J. Weakley, J. L. Cohn, and R. Sharma, Structural properties and thermal conductivity of crystalline Ge clathrates, Physical Review B 61, 3845 (2000).

G. S. Nolas, T. J. Weakley, and J. L. Cohn, Structural, chemical and transport properties of a new clathrate compound: Cs₈Zn₄Sn₄₂, Chemistry of Materials 1, 2470 (1999).

J. L. Cohn, G. S. Nolas, V. Fessatidis, T. H. Metcalf, and G. A. Slack, Glasslike Heat Conduction in High-Mobility Crystalline Semiconductors, Physical Review Letters 82, 779 (1999).

G. S. Nolas, J. L. Cohn, G. A. Slack, and S. B. Schujman, Semiconducting Ge clathrates: Promising candidates for thermoelectric applications, Applied Physics Letters 73, 178 (1998).