Lambda point

[1] The highest pressure at which He-I and He-II can coexist is the bcc−He-I−He-II triple point with a helium solid at 1.762 K (−271.388 °C), 29.725 atm (3,011.9 kPa).[2] The point's name derives from the graph (pictured) that results from plotting the specific heat capacity as a function of temperature (for a given pressure in the above range, in the example shown, at 1 atmosphere), which resembles the Greek letter lambdaThe tip of the peak is so sharp that a critical exponent characterizing the divergence of the heat capacity can be measured precisely only in zero gravity, to provide a uniform density over a substantial volume of fluid.Hence, the heat capacity was measured within 2 nK below the transition in an experiment included in a Space Shuttle payload in 1992.[3] Although the heat capacity has a peak, it does not tend towards infinity (contrary to what the graph may suggest), but has finite limiting values when approaching the transition from above and below.[6] The quoted experimental value of α is in a significant disagreement[7][4] with the most precise theoretical determinations[8][9][10] coming from high temperature expansion techniques, Monte Carlo methods and the conformal bootstrap.
The plot of the specific heat capacity versus temperature.
temperatureheliumsuperfluidhelium IIatmospheretriple pointvapor pressurehermeticspecific heat capacitylambdaSpace Shuttle(more unsolved problems in physics)infinitycritical exponentMonte Carloconformal bootstrapLambda point refrigeratorJournal of Physical and Chemical Reference DataBibcodeJournal of Low Temperature PhysicsPhysical Review Lettersthe liquid-vapor critical pointIsing critical exponentsStates of matterLiquidSupercritical fluidPlasmaBose–Einstein condensateFermionic condensateDegenerate matterQuantum HallRydberg matterStrange matterSupersolidPhotonic moleculeQCD matterQuark–gluon plasmaColor-glass condensateColloidCrystalLiquid crystalTime crystalQuantum spin liquidExotic matterProgrammable matterDark matterAntimatterAntiferromagnetFerrimagnetFerromagnetString-net liquidSuperglassPhase transitionsBoilingBoiling pointCondensationCritical lineCritical pointCrystallizationDepositionEvaporationFlash evaporationFreezingChemical ionizationIonizationMeltingMelting pointRecombinationRegelationSaturated fluidSublimationSupercoolingVaporizationVitrificationEnthalpy of fusionEnthalpy of sublimationEnthalpy of vaporizationLatent heatLatent internal energyTrouton's ruleVolatilityBaryonic matterBinodalCompressed fluidCooling curveEquation of stateLeidenfrost effectMacroscopic quantum phenomenaMpemba effectOrder and disorder (physics)SpinodalSuperconductivitySuperheated vaporSuperheatingThermo-dielectric effect